Technology Transfer Network / NAAQS
Ozone Implementation
Ambient Air Quality Surveillance Siting
Criteria for Open Path Analyzers
Note: EPA no longer updates this information, but it may be useful as a reference or resource.
[Federal Register: October 6, 1995 (Volume 60, Number 194)]
[Rules and Regulations]
[Page 52315-52329]
>From the Federal Register Online via GPO Access [wais.access.gpo.gov]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 58
[FRL-5304-9]
RIN 2060-AF88
Ambient Air Quality Surveillance Siting Criteria for Open Path
Analyzers
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: EPA is amending its regulations to define the appropriate
ambient air monitoring criteria for open path (long-path) analyzers.
These revisions to the Ambient Air Quality Surveillance regulations
define the siting requirements for open path analyzers used as State
and Local Air Monitoring Stations (SLAMS), National Air Monitoring
Stations (NAMS) and Photochemical Assessment Monitoring Stations
(PAMS), as well as general quality assurance procedures for this
technology. These changes provide the ambient air monitoring community
with criteria needed to effectively use open path analyzers and
associated data for regulatory purposes.
EFFECTIVE DATE: This final rule and all contained regulatory changes
except for appendix D, section 2.2, are effective on October 6, 1995.
The 40 CFR part 58, appendix D, section 2.2 requirements are not
effective until the Office of Management and Budget approves the
information requirements contained in them and the EPA publishes a
document announcing their approval in the Federal Register.
ADDRESSES: Copies of the comments received on the notice of proposed
rulemaking, supporting documentation, and the response to public
comments document may be obtained from: Air Docket (LE-131), Attention:
Docket Number A-93-44, U.S. Environmental Protection Agency, room M-
1500, 401 M Street, SW., Washington, D.C. 20460. Docket Number A-93-44,
containing supporting information used in developing these revised
regulations, is available for public inspection and copying between
8:30 a.m. and 12 noon, and between 1:30 p.m. and 3:30 p.m., Monday
through Friday, at the EPA's Air Docket Section at the address noted
above. As provided in 40 CFR part 2, a reasonable fee may be charged
for copying.
FOR FURTHER INFORMATION CONTACT: Lee Ann B. Byrd (919) 541-5367,
Monitoring and Quality Assurance Group (MD-14), Office of Air Quality
Planning and Standards, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711.
SUPPLEMENTARY INFORMATION:
Table of Contents
I. Authority
II. Background
III. Discussion of Regulatory Revisions and Major Comments on
Proposal
A. Section 58.1 Definitions
B. Appendix A--Quality Assurance Requirements for State and
Local Air Monitoring Stations (SLAMS)
C. Appendix B--Quality Assurance Requirements for Prevention of
Significant Deterioration (PSD) Air Monitoring
D. Appendix D--Network Design Criteria for State and Local Air
Monitoring Stations (SLAMS), National Air Monitoring Stations
(NAMS), and Photochemical Assessment Monitoring Stations (PAMS)
E. Appendix E--Probe and Path Siting Criteria for Ambient Air
Quality Monitoring
IV. Administrative Requirements
A. Administrative Designation
B. Reporting and Recordkeeping Requirements
C. Regulatory Flexibility Act
D. Unfunded Mandates Reform Act of 1995
I. Authority
Sections 110, 301(a), 313, and 319 of the Clean Air Act as amended
42 U.S.C. 7410, 7601(a), 7613, 7619.
II. Background
A new technique for monitoring pollutants in ambient air has been
developed and introduced to the EPA. Instruments based on this new
technique, called open path (or long-path) analyzers, use ultraviolet,
visible, or infrared light to measure nitrogen dioxide (NO2),
ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), and
other gaseous pollutant concentrations over a path of several meters up
to several kilometers. The measurements obtained by these open path
analyzers are path-integrated values from which path-averaged
concentrations are obtained. In contrast, traditional point analyzers
measure pollutant concentrations at one specific point by extracting an
air sample from the atmosphere through an inlet probe.
Due to the fundamental difference in the measurement principles of
open path and point analyzers, there may be tradeoffs in using each
type of instrument for certain applications. Because of the ability of
open path analyzers to measure pollutant concentrations over a path,
these new techniques are expected to provide better spatial coverage,
and thereby a better assessment of a general population's exposure to
air pollutants for certain applications. However, due to this same
path-averaging characteristic, open path analyzers could underestimate
high pollutant concentrations at specific points within the measurement
path for other ambient air monitoring situations. The applicability of
either technique to a particular monitoring scenario is dependent on a
number of factors including plume dispersion characteristics,
monitoring location, pollutant of interest, population density, site
topography, and monitoring objective. The EPA has considered these
factors in evaluating the advantages and disadvantages of using open
path analyzers for the various ambient air monitoring applications
detailed in 40 CFR part 58.
The EPA has assessed the performance of an open path analyzer as
candidate equivalent methods for measuring ozone, sulfur dioxide, and
nitrogen dioxide under part 53. This open path analyzer was formally
designated as an equivalent method for each of the three pollutants in
a Federal Register notice, volume 60, number 84 on May 2, 1995. In
parallel with this effort, the EPA developed these part 58 siting and
quality assurance criteria for open path analyzers, which were
published on August 18, 1994 as a notice of proposed rulemaking.
The intended purpose of these revisions to part 58 is to define
first the conceptual framework of network design and siting which is
equally relevant to open path and point types of ambient air monitoring
sites, followed by the practical implications that flow from the
conceptual approach. Comments received in response to the notice of
proposed rulemaking have been carefully considered. Improvements to the
network design and siting criteria were identified from these comments,
and, as appropriate,
[[Page 52316]]
were incorporated into the regulatory text as detailed in this action.
Copies of the specific EPA responses to each comment received are
available in the docket as noted previously.
III. Discussion of Regulatory Revisions and Major Comments on Proposal
A. Section 58.1 Definitions
Today's action adds several new definitions to part 58 which are
needed to clearly define the proposed new requirements for open path
analyzers. Definitions for ``point analyzer'' and ``open path
analyzer'' have been added to define these two types of automated
instruments and to clarify the distinction between them, since the
various new and existing requirements may apply to one or the other or
both types of analyzers. A new definition for ``probe'' is added to
specify the inlet where an air sample is extracted from the atmosphere
for delivery to a sampler or point analyzer. Similarly, a new
definition is added for ``monitoring path'' to describe the path in the
atmosphere over which an open path analyzer measures and averages a
pollutant concentration. Closely associated with the term ``monitoring
path'' are new definitions for ``monitoring path length,'' to describe
the scalar length of the monitoring path, and ``optical measurement
path length,'' to describe the actual length of the optical beam of an
open path instrument. The length of the optical beam may be two or more
times the length of the monitoring path when one or more mirrors are
used to cause the optical beam to pass through the monitoring path more
than once. One public comment recommended changes to the language of
the two former definitions to clarify the differences between path
integrated values and path-averaged concentrations. The EPA concurs
with this recommendation and clarifying language has been added.
To help describe the new requirements for data quality assessment
procedures, the term ``effective concentration'' is defined. This term
refers to the ambient concentration of a pollutant over the monitoring
path that would be equivalent to a much higher concentration of the
pollutant contained in a short calibration cell inserted into the
optical beam of an open path analyzer during a precision test or
accuracy audit. Specifically, effective concentration is defined as the
actual concentration of the pollutant in the test cell multiplied by
the ratio of the optical measurement path length of the test cell to
the optical measurement path length of the atmospheric monitoring path.
Also, when a calibration cell is inserted into the actual atmospheric
measurement beam of an open path analyzer for a precision or accuracy
test, the resulting measurement reading would be the sum of the
pollutant concentration in the calibration cell and the pollutant
concentration in the atmosphere. The atmospheric pollutant
concentration must be measured separately and subtracted from the test
measurement to produce a ``corrected concentration,'' which would be
the true test result. Thus, the term ``corrected concentration'' is
defined as the result of such a precision or accuracy assessment test
after correction of the test measurement by subtracting the atmospheric
pollutant concentration.
Finally, a formal definition of ``monitor'' is provided to clarify
its use in the regulations as a generic term to refer to any type of
ambient air analyzer or sampler that is acceptable for use in a SLAMS
monitoring network under appendix C of this part. A monitor could thus
be a point analyzer, an open path analyzer, or a sampler.
B. Appendix A--Quality Assurance Requirements for SLAMS
Appendix A describes both general quality assurance requirements
applicable to SLAMS air monitoring as well as specific procedures for
assessing the quality of the monitoring data obtained in SLAMS
monitoring networks. While the general quality assurance requirements
(in section 2) are directly applicable to open path analyzers without
change, the more specific data quality assessment procedures (in
section 3) must be modified somewhat to apply to open path analyzers.
Accordingly, changes to these procedures are provided to incorporate
appropriate data quality assessment tests applicable to open path
monitoring instruments. To the extent possible, the new requirements
are similar or parallel to the existing requirements for point
analyzers.
For both the precision test (section 3.1) and the accuracy audit
(section 3.2), the new requirements specify that an optical calibration
or test cell containing a pollutant concentration standard must be
inserted into the optical measurement beam of the open path analyzer.
Both theory and testing indicate that the use of such a calibration or
test cell is equivalent in accuracy to measurement of the equivalent
pollutant concentration in air over the entire monitoring path of an
open path analyzer. Each concentration standard must be selected such
that it produces an ``effective concentration'' equivalent to a
specified ambient concentration over the monitoring path. As noted
previously, effective concentration is defined as the actual
concentration of the pollutant in the test cell multiplied by the ratio
of the optical measurement path length of the test cell to the optical
measurement path length of the atmospheric monitoring path. The
effective concentrations specified for the precision and accuracy tests
for open path analyzers are the same as the test concentrations
currently specified in these procedures for point analyzers.
Ideally, precision and accuracy assessments should test a
monitoring instrument in its normal monitoring configuration.
Therefore, the new test procedures require that the test or calibration
cell containing the test pollutant concentration standard be inserted
into the actual atmospheric measurement beam of the open path analyzer.
The resulting test measurement of the pollutant concentration is thus
the sum of the test concentration in the cell and the pollutant
concentration in the atmosphere, because the measurement beam would
pass through both the test cell and the atmospheric monitoring path.
Accordingly, a correction for the atmospheric concentration is required
to obtain the true test result. In the new procedures, the atmospheric
pollutant concentration is measured immediately before and again
immediately after the precision or accuracy test, and the average of
these two measurements is subtracted from the test concentration
measurement to produce a ``corrected concentration,'' which is reported
as the test result. One comment was received regarding the former
correction procedure which indicated a concern that a second, point
analyzer would be needed to complete the accuracy audit and precision
check procedures described in the proposal. The accuracy audit and
precision check procedures defined in this action do not require the
use of a second point analyzer. It is intended that the ambient air
concentration measurements needed to correct the test readings would be
obtained by the open path analyzer under test. The language of the
procedures has been changed to clarify this requirement.
The corrected concentration reported for a precision or accuracy
test may not be accurate if the atmospheric pollutant concentration
changes during the test. When the ambient concentration is variable,
the average of the pre- and post-test measurements may not be an
accurate representation of the ambient pollutant concentration during
the test.
[[Page 52317]]
The proposed test procedures recommend that these tests should be
carried out, if possible, during periods when the atmospheric pollutant
concentration is low and steady. The lower the atmospheric pollutant
concentration, the steadier the concentration is likely to be and the
better the pre- and post-test measurements will represent the actual
atmospheric concentration during the test measurement. Further, the
procedures provide that if the pre- and post-test measurements of the
atmospheric concentration differ by more than 20 percent of the
effective concentration of the test standard, the test result is
discarded and the test repeated.
Two comments were received regarding the recommendation that pre-
and post-test measurements be taken when the atmospheric pollutant
concentration is low and steady, such as during early morning or late
evening hours. These comments illustrated a concern that it may be
difficult for a monitoring agency to conduct the accuracy audits and
precision checks at such specific times. In amending the monitoring
regulations to permit the use of open path analyzers, the EPA is not
suggesting that the use of open path analyzers is necessarily cost
effective or even necessarily advantageous. The EPA is permitting their
use, at the discretion of the monitoring agency, for whatever benefit
the agency may believe to accrue. The recommendation cited is intended
to point out that the precision and accuracy test results may be better
if carried out during periods when concentration levels are more likely
to be low and steady, and therefore the timing of these tests as to the
time of day or the meteorological conditions of the day should be
considered--to the extent practicable--by the monitoring agency
scheduling these tests.
A comment was received which recommended that accuracy limits on
the measurement of the optical measurement path length be incorporated
into the regulation. This issue of the determination of the optical
measurement path length is particularly important because an error in
this parameter would not normally be compensated for in the calibration
or be evident in the results of the accuracy audit procedures for open
path analyzers. Therefore, the accuracy audit procedure has been
revised to include reverification of this parameter.
It is recognized that the new tests for precision and accuracy for
open path analyzers, as well as the existing tests for point analyzers,
are described in very general terms, and that additional, more detailed
information and guidance are usually necessary for an analyzer operator
to carry out these tests properly. Accordingly, section 3 of appendix A
is amended by adding an explicit indication that supplemental
information and guidance to assist the analyst in conducting these
tests may be available in the publication, ``Quality Assurance Handbook
for Air Pollution Measurement Systems, Volume II'' (EPA-600/4-77-027a,
identified as Reference 3 at the end of appendix A), or in the
operation or instruction manual associated with the particular monitor
being used.
The techniques for precision and accuracy assessment of open path
analyzers are based largely on consultations with the manufacturer,
along with EPA tests, of the differential optical absorption
spectrometer that is currently under consideration by the EPA for
possible designation as equivalent methods under 40 CFR part 53.
However, it is desirable that the techniques be generic in nature, if
possible, so that they would be applicable to other types of open path
monitoring instruments as well. In addition, for some types of open
path instruments or for some installations or configurations, there may
be technical reasons why the new techniques for precision and accuracy
assessment may not be feasible, appropriate, or advisable. As a result,
these procedures allow for the use of an alternate local light source
or an alternate optical path that does not include the normal
atmospheric monitoring path, if such an alternate configuration is
permitted by the operation or instruction manual associated with the
analyzer. Since the analyzer operation or instruction manual would be
subject to approval as part of the requirements for EPA designation of
an open path analyzer as an equivalent method, the EPA would thereby
have control over the alternate configurations that would be allowable
for the precision and accuracy assessment tests.
One comment was received recommending more details be provided
within the regulation defining the limitations and conditions under
which an alternative light source could be used. Because it is
impossible to anticipate the variety of open path analyzers and audit
techniques that could eventually be used, it is difficult, if not
impossible, to define specific limits and conditions under which an
alternative light source could be permitted for accuracy audits and
precision checks. The specific authorization to use an alternate light
source will be determined on a case-by-case basis for each specific
open path analyzer subject to an equivalent method determination under
part 53. Then, if permitted, the analyzer-specific conditions and
limitations for its use would be described in detail in the associated
operation/instruction manual. This manual is approved as part of the
formal designation of the analyzer as an equivalent method, and the EPA
can make sure that the procedures and conditions are addressed
adequately in the manual before a candidate method is designated as an
equivalent method.
C. Appendix B--Quality Assurance Requirements for Prevention of
Significant Deterioration (PSD) Air Monitoring
Appendix B sets forth both general quality assurance requirements
for PSD monitoring as well as specific procedures for assessing the
quality of the monitoring data obtained in PSD monitoring networks. The
amendments and procedures proposed for appendix B to extend the
existing requirements to open path analyzers are essentially identical
to the changes proposed for appendix A. Similarly, changes to the
regulatory language resulting from public comments received on appendix
A apply equally to appendix B.
D. Appendix D--Network Design for State and Local Air Monitoring
Stations (SLAMS), National Air Monitoring Stations (NAMS), and
Photochemical Air Monitoring Stations (PAMS)
Changes to appendix D were not recommended with the original
proposal associated with this action. Public comments indicated the
need for the EPA to consider the comparability of data collected by
point analyzers and data collected by open path analyzers, particularly
in situations of nonuniform pollutant concentrations. This issue also
raises an additional concern over introducing new ambient air
monitoring technologies into the Nation's monitoring program which is
currently based on traditional point-specific monitoring techniques,
and its impact on existing air quality management programs.
In response to these issues, the EPA has modified appendix D with
criteria and requirements intended to help agencies determine what, if
any, impacts the introduction of this technology may have on their
local air quality management programs. These criteria include
investigations into the specific technology selected for a chosen
application, the site location with respect to the monitoring
objective, and a requirement for concurrent
[[Page 52318]]
monitoring when replacing an existing monitor with one using a
different ambient air monitoring technique. The intent of the latter
requirement is to provide a bridge between the two types of ambient air
monitoring data (point and path-averaged values).
The EPA recognizes that these appendix D requirements can be more
effectively and efficiently used to improve an ambient air monitoring
network if consideration for the particular monitoring site, objective,
and related conditions is included in the network analysis. As a
result, these requirements are presented in general terms, with waiver
provisions provided as appropriate.
E. Appendix E--Probe and Path Siting Criteria for Ambient Air Quality
Monitoring
This action amends appendix E by adding new siting criteria
applicable to open path analyzers for monitoring of SO2, O3,
NO2, CO, and O3 precursors (defined in the PAMS program as
volatile organic compounds, oxides of nitrogen, and selected
carbonyls). Because of the substantial similarity in the siting
criteria for SO2, O3, and NO2 (both the existing
criteria for point monitors and proposed new criteria for open path
analyzers), the siting requirements for these three pollutants are
combined, consolidated, and set forth in section 2 of appendix E. As a
result, the existing criteria for SO2, O3, and NO2 in
sections 3, 5, and 6 are deleted, and those sections are reserved. As
noted below, the criteria for CO monitoring are somewhat different, so
they are retained in a separate section 4. Siting criteria for
measuring O3 and its precursors as part of a PAMS network are
included in section 10. In all cases, the new open path provisions have
been incorporated into the existing provisions, as appropriate.
The new open path siting requirements largely parallel the existing
requirements for point analyzers, with the revised provisions
applicable to either a ``probe'' (for point analyzers), a ``monitoring
path'' (for open path analyzers), or both, as appropriate. Accordingly,
criteria for the monitoring path of an open path analyzer are described
for horizontal and vertical placement, spacing from minor sources,
spacing from obstructions, spacing from trees, and spacing from
roadways. The open path requirements apply to most of the monitoring
path.generally 80 or 90 percent.but not to the entire monitoring path,
to allow some needed flexibility in siting open path analyzers. For
example, using the proposed 80 percent requirement, a monitoring path
may be sited across uneven terrain, where up to 20 percent of the
monitoring path may not fall within the proposed 3- to-15 meter
specification for height above ground.
Two comments were received on the optical obstructions, or physical
interferences (e.g., rain, snow, fog) criteria discussed in sections
2.3, 4.2, and 10.2 of the proposed rule. The specific open path
analyzer currently under consideration for designation as an equivalent
method calculates the level of uncertainty for each data value obtained
based on several factors including diminished light levels due to
optical obstructions. These uncertainty levels may be used to
invalidate data that are outside of established error acceptance
levels. Invalidating these data will have an effect on the data capture
percentages, and potentially, on the database's ability to properly
characterize air quality for a given region. Because of this
possibility, recommendations for conducting analyses of obscuration
potential and its resulting effect on the representativeness of the
data record have been included in sections 2.3, 4.2, and 10.2 of
appendix E.
In addition to the criteria common to both point and open path
analyzers mentioned above, two new provisions, applicable only to open
path analyzers, are included which limit the maximum length of the
monitoring path and the cumulative interferences on the path. The
maximum monitoring path length limit helps to ensure that open path
monitoring data represent the air volume that they are intended to
measure according to the monitoring objectives of the spatial scale
identified for the site. Similarly, the limit for the cumulative
interferences on the monitoring path controls the total amount of
interference from minor sources, roadways, obstructions, and other
factors that might unduly influence the monitoring data collected by an
open path analyzer. This limit is necessary because a long monitoring
path presents a much greater opportunity to be affected by multiple
interferences.
In the consolidation of current sections 3, 5, and 6 to section 2,
Tables 2 and 3, which list the minimum separation distances between
O3 and NO2 stations and nearby roadways, are combined and
redesignated as Table 1. As a result, Table 1 (in section 3), Table 4
(in section 7), Table 5 (in section 10), and Table 6 (in section 12)
are renumbered as Tables 2, 3, 4, and 5, respectively. Finally, the
summary of all the general siting requirements in renumbered Table 5 is
modified to include the new criteria for monitoring paths.
IV. Administrative Requirements
A. Administrative Designation
1. Executive Order 12866
Under Executive Order 12866 (58 FR 51735 (October 4, 1993)) the
Agency must determine whether the regulatory action is ``significant''
and therefore subject to Office of Management and Budget (OMB) review
and to the requirements of the Executive Order. The Order defines
``significant regulatory action'' as one that is likely to result in a
rule that may:
(1) Have an annual effect on the economy of $100 million or more or
adversely affect in a material way the economy, a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or State, local, or tribal governments or
communities;
(2) Create a serious inconsistency or otherwise interfere with an
action taken or planned by another Agency;
(3) Materially alter the budgetary impact of entitlements, grants,
user fees, or loan programs or the rights and obligations or recipients
thereof; or
(4) Raise novel legal or policy issues arising out of legal
mandates, the President's priorities, or the principles set forth in
the Executive Order.
It has been determined that this rule is not a ``significant
regulatory action'' under the terms of Executive Order 12866 and is
therefore not subject to OMB review.
2. Enhancing the Intergovernmental Partnership Under Executive Order
12875
In compliance with Executive Order 12875, we have involved State
and local governments in the development of this rule. To accomplish
this effort, we have presented information on the new open path
analyzer technology at various national and international technical
symposiums, such as the Air and Waste Management Association specialty
conferences, which were attended by several State and local agencies.
We have presented information and solicited comment from State and
local ambient air monitoring agencies on the use of this new technology
and the contents of this rule through forums such as the Standing Air
Monitoring Work Group. This work group, which consists of various State
and local agency and EPA representatives, is designed to provide a
strategic vision and direction for the ambient air monitoring programs
within the nation.
[[Page 52319]]
In evaluating open path analyzers, we have conducted joint methodology
experiments in various locations with the States of Connecticut,
Georgia, Florida, and Texas.
B. Reporting and Recordkeeping Requirements
The information collection requirements contained in this rule have
been submitted for approval to OMB under the Paperwork Reduction Act,
44 U.S.C. 3501 et seq. An Information Collection Request document has
been prepared by the EPA (ICR No. 0940.12) and a copy may be obtained
from Sandy Farmer, Information Policy Branch, EPA, 401 M Street S.W.,
Mail Code 2136, Washington, D.C. 20460; or by calling (202) 260-2740.
These requirements are not effective until OMB approves them and a
technical amendment to that effect is published in the Federal
Register.
This collection of information has an estimated reporting burden
averaging 300 hours per response and an estimated annual recordkeeping
burden averaging 24 hours per respondent. These estimates include time
for reviewing instructions, searching existing data sources, gathering
and maintaining the data needed, and completing and reviewing the
collection of information.
Send comments regarding the burden estimate or any other aspect of
this collection of information, including suggestions for reducing this
burden to Chief, Information Policy Branch, EPA, 401 M Street S.W.,
Mail Code 2136, Washington, D.C. 20460, and to the Office of
Information and Regulatory Affairs, Office of Management and Budget,
Washington, D.C. 20503, marked ``Attention: Desk Officer for EPA.
C. Regulatory Flexibility Act
Pursuant to section 605(b) of the Regulatory Flexibility Act, 5
U.S.C. 605(b), the Administrator certifies that this rule will not have
a significant economic impact on a substantial number of small
entities. This rulemaking package does not impose any additional
requirements on small entities, rather, it is this action's intent to
provide all entities with the option to choose the most suitable
ambient air method for their particular application. This proposal
provides the appropriate siting and quality assurance criteria for a
new ambient air monitoring technology (open path analyzers) as they are
used in various applications. The criteria listed in this rulemaking
package parallel existing requirements and vary only as necessary due
to technological differences between measurement techniques. It is
possible that a beneficial impact may be encountered by some small
entities that use this new technology in certain scenarios.
D. Unfunded Mandates Reform Act of 1995
Under sections 202, 203 and 205 of the Unfunded Mandates Reform Act
of 1995 (``Unfunded Mandates Act''), signed into law on March 22, 1995,
the EPA must undertake various actions in association with proposed or
final rules that include a Federal mandate that may result in estimated
costs of $100 million or more to the private sector, or to State,
local, or tribal governments in the aggregate.
The EPA's final action does not impose any federal
intergovernmental mandate, as defined in section 101 of the Unfunded
Mandates Act, upon any State, local, or tribal government. This action
gives these entities an opportunity to choose the most suitable ambient
air quality monitoring method for their program, but does mandate any
particular method. Finally, the EPA has determined that this action
does not include a mandate that may result in estimated costs of $100
million or more to State, local, or tribal governments in the
aggregate. This action does not directly affect the private sector.
List of Subjects in 40 CFR Part 58
Environmental Protection, Air pollution control, Ambient air
monitoring, Ambient air pollutant measurements, Ambient air monitoring
networks and siting criteria, Ambient data, Intergovernmental
relations, National ambient air monitoring program, Open path
analyzers, Optical sensing, Quality assurance requirements, Reporting
and recordkeeping requirements, State and local agency ambient air
monitoring programs.
Dated: September 21, 1995.
Carol M. Browner,
Administrator.
For reasons set forth in the preamble, title 40, chapter I, part 58
of the Code of Federal Regulations is amended as follows:
PART 58--[AMENDED]
1. The authority citation for part 58 continues to read as follows:
Authority: 42 U.S.C. 7410, 7601(a), 7613, and 7619.
2. In Sec. 58.1 paragraphs (aa) through (ii) are added to read as
follows:
Sec. 58.1 Definitions.
* * * * *
(aa) Point analyzer is an automated analytical method that measures
pollutant concentration in an ambient air sample extracted from the
atmosphere at a specific inlet probe point and that has been designated
as a reference or equivalent method in accordance with part 53 of this
chapter.
(bb) Probe is the actual inlet where an air sample is extracted
from the atmosphere for delivery to a sampler or point analyzer for
pollutant analysis.
(cc) Open path analyzer is an automated analytical method that
measures the average atmospheric pollutant concentration in situ along
one or more monitoring paths having a monitoring path length of 5
meters or more and that has been designated as a reference or
equivalent method under the provisions of part 53 of this chapter.
(dd) Monitoring path for an open path analyzer is the actual path
in space between two geographical locations over which the pollutant
concentration is measured and averaged.
(ee) Monitoring path length of an open path analyzer is the length
of the monitoring path in the atmosphere over which the average
pollutant concentration measurement (path-averaged concentration) is
determined. See also, optical measurement path length.
(ff) Optical measurement path length is the actual length of the
optical beam over which measurement of the pollutant is determined. The
path-integrated pollutant concentration measured by the analyzer is
divided by the optical measurement path length to determine the path-
averaged concentration. Generally, the optical measurement path length
is:
(1) Equal to the monitoring path length for a (bistatic) system
having a transmitter and a receiver at opposite ends of the monitoring
path;
(2) Equal to twice the monitoring path length for a (monostatic)
system having a transmitter and receiver at one end of the monitoring
path and a mirror or retroreflector at the other end; or
(3) Equal to some multiple of the monitoring path length for more
complex systems having multiple passes of the measurement beam through
the monitoring path.
(gg) Effective concentration pertains to testing an open path
analyzer with a high-concentration calibration or audit standard gas
contained in a short test cell inserted into the optical measurement
beam of the instrument. Effective concentration is the equivalent
ambient-level concentration that would produce the same spectral
absorbance
[[Page 52320]]
over the actual atmospheric monitoring path length as produced by the
high-concentration gas in the short test cell. Quantitatively,
effective concentration is equal to the actual concentration of the gas
standard in the test cell multiplied by the ratio of the path length of
the test cell to the actual atmospheric monitoring path length.
(hh) Corrected concentration pertains to the result of an accuracy
or precision assessment test of an open path analyzer in which a high-
concentration test or audit standard gas contained in a short test cell
is inserted into the optical measurement beam of the instrument. When
the pollutant concentration measured by the analyzer in such a test
includes both the pollutant concentration in the test cell and the
concentration in the atmosphere, the atmospheric pollutant
concentration must be subtracted from the test measurement to obtain
the corrected concentration test result. The corrected concentration is
equal to the measured concentration minus the average of the
atmospheric pollutant concentrations measured (without the test cell)
immediately before and immediately after the test.
(ii) Monitor is a generic term for an instrument, sampler,
analyzer, or other device that measures or assists in the measurement
of atmospheric air pollutants and which is acceptable for use in
ambient air surveillance under the provisions of appendix C to this
part, including both point and open path analyzers that have been
designated as either reference or equivalent methods under part 53 of
this chapter and air samplers that are specified as part of a manual
method that has been designated as a reference or equivalent method
under part 53 of this chapter.
3. Appendix A is amended as follows:
a. The fourth paragraph of section 3 introductory text is revised.
b. Section 3.1 is revised.
c. The text preceding the table in the second paragraph, and the
seventh, and eighth paragraphs of section 3.2 are revised; and a new
paragraph is added between the seventh and eighth paragraphs.
d. Table A-1 is revised.
Appendix A--Quality Assurance Requirements for State and Local Air
Monitoring Stations (SLAMS)
* * * * *
3. Data Quality Assessment Requirements
* * * * *
Assessment results shall be reported as specified in section 4.
Concentration and flow standards must be as specified in sections 2.3
or 3.4. In addition, working standards and equipment used for accuracy
audits must not be the same standards and equipment used for routine
calibrations. Additional information and guidance in the technical
aspects of conducting these tests may be found in Reference 3 or in the
operation or instruction manual associated with the analyzer or
sampler. Concentration measurements reported from analyzers or
analytical systems (indicated concentrations) should be based on stable
readings and must be derived by means of the same calibration curve and
data processing system used to obtain the routine air monitoring data
(see Reference 1 and Reference 3, section 2.0.9.1.3(d)). Table A-1
provides a summary of the minimum data quality assessment requirements,
which are described in more detail in the following sections.
3.1 Precision of Automated Methods
A one-point precision check must be carried out at least once every
two weeks on each automated analyzer used to measure SO2,
NO2, O3, and CO. The precision check is made by challenging
the analyzer with a precision check gas of known concentration
(effective concentration for open path analyzers) between 0.08 and 0.10
ppm for SO2, NO2, and O3 analyzers, and between 8 and 10
ppm for CO analyzers. To check the precision of SLAMS analyzers
operating on ranges higher than 0 to 1.0 ppm SO2, NO2, and
O3, or 0 to 100 ppm for CO, use precision check gases of
appropriately higher concentration as approved by the appropriate
Regional Administrator or the Regional Administrator's designee.
However, the results of precision checks at concentration levels other
than those specified above do not need be reported to the EPA. The
standards from which precision check test concentrations are obtained
must meet the specifications of section 2.3.
Except for certain CO analyzers described below, point analyzers
must operate in their normal sampling mode during the precision check,
and the test atmosphere must pass through all filters, scrubbers,
conditioners, and other components used during normal ambient sampling
and as much of the ambient air inlet system as is practicable. If
permitted by the associated operation or instruction manual, a CO point
analyzer may be temporarily modified during the precision check to
reduce vent or purge flows, or the test atmosphere may enter the
analyzer at a point other than the normal sample inlet, provided that
the analyzer's response is not likely to be altered by these deviations
from the normal operational mode.
If a precision check is made in conjunction with a zero or span
adjustment, it must be made prior to such zero or span adjustments.
Randomization of the precision check with respect to time of day, day
of week, and routine service and adjustment is encouraged where
possible.
Open path analyzers are tested by inserting a test cell containing
a precision check gas concentration into the optical measurement beam
of the instrument. If possible, the normally used transmitter,
receiver, and, as appropriate, reflecting devices should be used during
the test, and the normal monitoring configuration of the instrument
should be altered as little as possible to accommodate the test cell
for the test. However, if permitted by the associated operation or
instruction manual, an alternate local light source or an alternate
optical path that does not include the normal atmospheric monitoring
path may be used. The actual concentration of the precision check gas
in the test cell must be selected to produce an ``effective
concentration'' in the range specified above. Generally, the precision
test concentration measurement will be the sum of the atmospheric
pollutant concentration and the precision test concentration. If so,
the result must be corrected to remove the atmospheric concentration
contribution. The ``corrected concentration'' is obtained by
subtracting the average of the atmospheric concentrations measured by
the open path instrument under test immediately before and immediately
after the precision check test from the precision test concentration
measurement. If the difference between these before and after
measurements is greater than 20 percent of the effective concentration
of the test gas, discard the test result and repeat the test. If
possible, open path analyzers should be tested during periods when the
atmospheric pollutant concentrations are relatively low and steady.
Report the actual concentration (effective concentration for open
path analyzers) of the precision check gas and the corresponding
concentration measurement (corrected concentration, if applicable, for
open path analyzers) indicated by the analyzer. The percent differences
between these concentrations are used to assess the precision of the
monitoring data as described in section 5.1.
3.2 Accuracy of Automated Methods
* * * * *
[[Page 52321]]
The audit is made by challenging the analyzer with at least one
audit gas of known concentration (effective concentration for open path
analyzers) from each of the following ranges that fall within the
measurement range of the analyzer being audited: * * *
* * * * *
For point analyzers, the audit shall be carried out by allowing the
analyzer to analyze the audit test atmosphere in its normal sampling
mode such that the test atmosphere passes through all filters,
scrubbers, conditioners, and other sample inlet components used during
normal ambient sampling and as much of the ambient air inlet system as
is practicable. The exception provided in section 3.1 for certain CO
analyzer does not apply for audits.
Open path analyzers are audited by inserting a test cell containing
the various audit gas concentrations into the optical measurement beam
of the instrument. If possible, the normally used transmitter,
receiver, and, as appropriate, reflecting devices should be used during
the audit, and the normal monitoring configuration of the instrument
should be modified as little as possible to accommodate the test cell
for the audit. However, if permitted by the associated operation or
instruction manual, an alternate local light source or an alternate
optical path that does not include the normal atmospheric monitoring
path may be used. The actual concentrations of the audit gas in the
test cell must be selected to produce ``effective concentrations'' in
the ranges specified in this section 3.2. Generally, each audit
concentration measurement result will be the sum of the atmospheric
pollutant concentration and the audit test concentration. If so, the
result must be corrected to remove the atmospheric concentration
contribution. The ``corrected concentration'' is obtained by
subtracting the average of the atmospheric concentrations measured by
the open path instrument under test immediately before and immediately
after the audit test (or preferably before and after each audit
concentration level) from the audit concentration measurement. If the
difference between the before and after measurements is greater than 20
percent of the effective concentration of the test gas standard,
discard the test result for that concentration level and repeat the
test for that level. If possible, open path analyzers should be audited
during periods when the atmospheric pollutant concentrations are
relatively low and steady. Also, the monitoring path length must be
reverified to within 3 percent to validate the audit, since
the monitoring path length is critical to the determination of the
effective concentration.
Report both the audit test concentrations (effective concentrations
for open path analyzers) and the corresponding concentration
measurements (corrected concentrations, if applicable, for open path
analyzers) indicated or produced by the analyzer being tested. The
percent differences between these concentrations are used to assess the
accuracy of the monitoring data as described in section 5.2.
* * * * *
Table A-1.--Minimum Data Assessment Requirements
----------------------------------------------------------------------------------------------------------------
Method Assessment method Coverage Minimum frequency Parameters reported
----------------------------------------------------------------------------------------------------------------
Precision:
Automated methods Response checks at Each analyzer........ Once per 2 weeks..... Actual concentration
for SO2, NO2, O3, concentration \2\ & measured
and CO. between .08 & .10 concentration.\3\
ppm (8 & 10 ppm for
CO) \2\.
Manual methods Collocated samplers.. 1 site for 1-5 sites; Once per week........ Two concentration
including lead. 2 sites for 6-20 measurements.
sites; 3 sites> 20
sites (sites with
highest conc.).
Accuracy:
Automated methods Response checks at: 1. Each analyzer. 2. 1. Once per year..... Actual concentration
for SO2, NO2, O3, .03-.08 ppm; 1,2 .15- 2512f analyzers (at 2. Each calendar \2\ & measured
and CO. .20 ppm; 1,2 .35-.45 least 1). quarter. (indicated)
ppm; 1,2 .80-.90 concentration \3\
ppm; 1,2 (If for each level.
applicable).
Manual methods for Check of analytical Analytical system.... Each day samples are Actual concentration
SO2 and NO2. procedure with audit analyzed, at least & measured
standard solutions. twice per quarter. (indicated)
concentration for
each audit
solution.
TSP, PM-10......... Check of sampler flow 1. Each sampler...... 1. Once per year..... Actual flow rate and
rate. 2. 2512f samplers 2. Each calendar flow rate indicated
(at least 1). quarter. by the sampler.
Lead............... 1. Check sample flow 1. Each sampler...... 1. Include with TSP.. 1. Same as for TSP.
rate as for TSP. 2. 2. Analytical system. 2. Each quarter...... 2. Actual
Check analytical concentration &
system with Pb audit measured
strips. (indicated)
concentration of
audit samples
(g Pb/
strip).
----------------------------------------------------------------------------------------------------------------
\1\ Concentration times 100 for CO.
\2\ Effective concentration for open path analyzers.
\3\ Corrected concentration, if applicable, for open path analyzers.
* * * * *
4. Appendix B is amended as follows:
a. The first paragraph of section 3 is revised.
b. Section 3.1 is revised.
c. The text preceding the table in the first paragraph, and the
third, and fourth paragraphs of section 3.2 are revised. A new
paragraph is added between the third and fourth paragraphs.
d. Table B-1 is revised.
[[Page 52322]]
Appendix B--Quality Assurance Requirements for Prevention of
Significant Deterioration (PSD) Air Monitoring
* * * * *
3. Data Quality Assessment Requirements
All ambient monitoring methods or analyzers used in PSD monitoring
shall be tested periodically, as described in this section 3, to
quantitatively assess the quality of the data being routinely
collected. The results of these tests shall be reported as specified in
section 6. Concentration standards used for the tests must be as
specified in section 2.3. Additional information and guidance in the
technical aspects of conducting these tests may be found in Reference 3
or in the operation or instruction manual associated with the analyzer
or sampler. Concentration measurements reported from analyzers or
analytical systems must be derived by means of the same calibration
curve and data processing system used to obtain the routine air
monitoring data. Table B-1 provides a summary of the minimum data
quality assessment requirements, which are described in more detail in
the following sections.
3.1 Precision of Automated Methods
A one-point precision check must be carried out at least once every
two weeks on each automated analyzer used to measure SO2,
NO2, O2, and CO. The precision check is made by challenging
the analyzer with a precision check gas of known concentration
(effective concentration for open path analyzers) between 0.08 and 0.10
ppm for SO2, NO2, and O3 analyzers, and between 8 and 10
ppm for CO analyzers. The standards from which precision check test
concentrations are obtained must meet the specifications of section
2.3. Except for certain CO analyzers described below, point analyzers
must operate in their normal sampling mode during the precision check,
and the test atmosphere must pass through all filters, scrubbers,
conditioners and other components used during normal ambient sampling
and as much of the ambient air inlet system as is practicable. If
permitted by the associated operation or instruction manual, a CO point
analyzer may be temporarily modified during the precision check to
reduce vent or purge flows, or the test atmosphere may enter the
analyzer at a point other than the normal sample inlet, provided that
the analyzer's response is not likely to be altered by these deviations
from the normal operational mode.
Open path analyzers are tested by inserting a test cell containing
a precision check gas concentration into the optical measurement beam
of the instrument. If possible, the normally used transmitter,
receiver, and, as appropriate, reflecting devices should be used during
the test, and the normal monitoring configuration of the instrument
should be altered as little as possible to accommodate the test cell
for the test. However, if permitted by the associated operation or
instruction manual, an alternate local light source or an alternate
optical path that does not include the normal atmospheric monitoring
path may be used. The actual concentration of the precision check gas
in the test cell must be selected to produce an ``effective
concentration'' in the range specified above. Generally, the precision
test concentration measurement will be the sum of the atmospheric
pollutant concentration and the precision test concentration. If so,
the result must be corrected to remove the atmospheric concentration
contribution. The ``corrected concentration'' is obtained by
subtracting the average of the atmospheric concentrations measured by
the open path instrument under test immediately before and immediately
after the precision check test from the precision test concentration
measurement. If the difference between these before and after
measurements is greater than 20 percent of the effective concentration
of the test gas, discard the test result and repeat the test. If
possible, open path analyzers should be tested during periods when the
atmospheric pollutant concentrations are relatively low and steady.
If a precision check is made in conjunction with a zero or span
adjustment, it must be made prior to such zero or span adjustment. The
difference between the actual concentration (effective concentration
for open path analyzers) of the precision check gas and the
corresponding concentration measurement (corrected concentration, if
applicable, for open path analyzers) indicated by the analyzer is used
to assess the precision of the monitoring data as described in section
4.1. Report data only from automated analyzers that are approved for
use in the PSD network.
3.2 Accuracy of Automated Methods
Each sampling quarter, audit each analyzer that monitors for
SO2, NO2, O3, or CO at least once. The audit is made by
challenging the analyzer with at least one audit gas of known
concentration (effective concentration for open path analyzers) from
each of the following ranges that fall within the measurement range of
the analyzer being audited: * * *
* * * * *
For point analyzers, the audit shall be carried out by allowing the
analyzer to analyze the audit test atmosphere in the same manner as
described for precision checks in section 3.1. The exception given in
section 3.1 for certain CO analyzers does not apply for audits.
Open path analyzers are audited by inserting a test cell containing
an audit gas concentration into the optical measurement beam of the
instrument. If possible, the normally used transmitter, receiver, and,
as appropriate, reflecting devices should be used during the audit, and
the normal monitoring configuration of the instrument should be
modified as little as possible to accommodate the test cell for the
audit. However, if permitted by the associated operation or instruction
manual, an alternate local light source or an alternate optical path
that does not include the normal atmospheric monitoring path may be
used. The actual concentrations of the audit gas in the test cell must
be selected to produce ``effective concentrations'' in the range
specified in this section 3.2. Generally, each audit concentration
measurement result will be the sum of the atmospheric pollutant
concentration and the audit test concentration. If so, the result must
be corrected to remove the atmospheric concentration contribution. The
``corrected concentration'' is obtained by subtracting the average of
the atmospheric concentrations measured by the open path instrument
under test immediately before and immediately after the audit test (or
preferably before and after each audit concentration level) from the
audit concentration measurement. If the difference between these before
and after measurements is greater than 20 percent of the effective
concentration of the test gas standards, discard the test result for
that concentration level and repeat the test for that level. If
possible, open path analyzers should be audited during periods when the
atmospheric pollutant concentrations are relatively low and steady.
Also, the monitoring path length must be reverified to within
3 percent to validate the audit, since the monitoring path
length is critical to the determination of the effective concentration.
The differences between the actual concentrations (effective
concentrations for open path analyzers) of the audit test gas and the
corresponding concentration measurements (corrected
[[Page 52323]]
concentrations, if applicable, for open path analyzers) indicated by
the analyzer are used to assess the accuracy of the monitoring data as
described in section 4.2. Report data only from automated analyzers
that are approved for use in the PSD network.
* * * * *
Table B-1.--Minimum PSD Data Assessment Requirements
----------------------------------------------------------------------------------------------------------------
Method Assessment method Coverage Frequency Parameters reported
----------------------------------------------------------------------------------------------------------------
Precision:
Automated Methods Response check at Each analyzer........ Once per 2 weeks..... Actual concentration
for SO2, NO2, O3, concentration 2 & measured
and CO. between .08 & .10 concentration.3
ppm (8 & 10 ppm for
CO) 2.
TSP, PM10, Lead.... Collocated samplers.. Highest concentration Once per week or Two concentration
site in monitoring every 3rd day for measurements.
network. continuous sampling.
Accuracy:
Automated Methods Response check at: Each analyzer........ Once per sampling Actual
for SO2, NO2, O3, .03-.08 ppm;1,2 .15- quarter. concentration2 &
and CO. .20 ppm;1,2 .35-.45 measured
ppm;1,2 .80-.90 (indicated)
ppm;1,2 (if concentration3 for
applicable). each level.
TSP, PM10.......... Sampler flow check... Each sampler......... Once per sampling Actual flow rate and
quarter. flow rate indicated
by the sampler.
Lead............... 1. Sample flow rate 1. Each sampler...... 1. Once/quarter...... 1. Same as for TSP.
check.. 2. Analytical system. 2. Each quarter Pb 2. Actual
2. Check analytical samples are analyzed. concentration &
system with Pb audit measured
strips. concentration of
audit samples
(g Pb/
strip).
----------------------------------------------------------------------------------------------------------------
\1\ Concentration shown times 100 for CO.
\2\ Effective concentration for open path analyzers.
\3\ Corrected concentration, if applicable, for open path analyzers.
* * * * *
5. Appendix D is amended as follows:
a. The second, third, and fourth paragraphs of section 1 are
revised; and a new paragraph is added between Table 1 and the last
paragraph of section 1.
b. Section 2.2 is added.
Appendix D--Network Design for State and Local Air Monitoring
Stations (SLAMS), National Air Monitoring Stations (NAMS), and
Photochemical Assessment Monitoring Stations (PAMS)
1. SLAMS Monitoring Objectives and Spatial Scales
* * * * *
The network of stations which comprise SLAMS should be designed to
meet a minimum of four basic monitoring objectives. These basic
monitoring objectives are: (1) To determine highest concentrations
expected to occur in the area covered by the network; (2) to determine
representative concentrations in areas of high population density; (3)
to determine the impact on ambient pollution levels of significant
sources or source categories; and (4) to determine general background
concentration levels. Of these four basic ambient air monitoring
network design objectives, attempts to measure in areas of maximum
concentrations and maximum population exposures (these can be exclusive
or coincident) are primary due to the combination of prevailing needs
and constraints.
It should be noted that this appendix contains no criteria for
determining the total number of stations in SLAMS networks, except that
a minimum number of lead SLAMS is prescribed. The optimum size of a
particular SLAMS network involves tradeoffs between data needs and
available resources which the EPA believes can best be resolved during
the network design process.
This appendix focuses on the relationship between monitoring
objectives and the geographical location of monitoring stations.
Included are a rationale and set of general criteria for identifying
candidate station locations in terms of physical characteristics which
most closely match a specific monitoring objective. The criteria for
more specifically siting the monitoring station, including spacing from
roadways and vertical and horizontal probe and path placement, are
described in appendix E of this part.
* * * * *
Open path analyzers can often be used effectively and
advantageously to provide better monitoring representation for
population exposure monitoring and general or background monitoring in
urban and neighborhood scales of representation. Such analyzers may
also be able to provide better area coverage or operational advantages
in high concentration and source-impact monitoring in middle scale and
possibly microscale areas. However, siting of open path analyzers for
the latter applications must be carried out with proper regard for the
specific monitoring objectives and for the path-averaging nature of
these analyzers. Monitoring path lengths need to be commensurate with
the intended scale of representativeness and located carefully with
respect to local sources or potential obstructions. For short-term/
high-concentration or source-oriented monitoring, the monitoring path
may need to be further restricted in length and be oriented
approximately radially with respect to the source in the downwind
direction, to provide adequate peak concentration sensitivity.
Alternatively, multiple (e.g., orthogonal) paths may be used
advantageously to obtain both wider area coverage and peak
concentration sensitivity. Further discussion on this topic is included
in section 2.2 of this appendix.
* * * * *
2. SLAMS Network Design Procedures
* * * * *
[[Page 52324]]
2.2 Substantive Changes in SLAMS/NAMS Network Design Elements
Two important purposes of the SLAMS monitoring data are to examine
and evaluate overall air quality within a certain region, and to assess
the trends in air pollutant levels over several years. The EPA believes
that one of the primary tools for providing these characterizations is
an ambient air monitoring program which implements technically
representative networks. The design of these networks must be carefully
evaluated not only at their outset, but at relatively frequent
intervals thereafter, using an appropriate combination of other
important technical tools, including: dispersion and receptor modeling,
saturation studies, point and area source emissions analyses, and
meteorological assessments. The impetus for these subsequent
reexaminations of monitoring network adequacy stems not only from the
need to evaluate the effect that changes in the environment may pose,
but also from the recognition that new and/or refined tools and
techniques for use in impact assessments are continually emerging and
available for application.
Substantiative changes to an ambient air monitoring network are
both inevitable and necessary; however, any changes in any substantive
aspect of an existing SLAMS network or monitoring site that might
affect the continuity or comparability of pollutant measurements over
time must be carefully and thoroughly considered. Such substantive
changes would include cessation of monitoring at an existing site,
relocation of an existing site, a change in the type of monitoring
method used, any change in the probe or path height or orientation that
might affect pollutant measurements, any significant changes in
calibration procedures or standards, any significant change in
operational or quality assurance procedures, any significant change in
the sources or the character of the area in the vicinity of a
monitoring site, or any other change that could potentially affect the
continuity or comparability of monitoring data obtained before and
after the change.
In general, these types of changes should be made cautiously with
due consideration given to the impact of such changes on the network/
site's ability to meet its intended goals. Some of these changes will
be inevitable (such as when a monitoring site will no longer be
available and the monitor must be relocated, for example). Other
changes may be deemed necessary and advantageous, after due
consideration of their impact, even though they may have a deleterious
effect on the long-term comparability of the monitoring data. In these
cases, an effort should be made to quantify, if possible, or at least
characterize, the nature or extent of the effects of the change on the
monitoring data. In all cases, the changes and all information
pertinent to the effect of the change should be properly and completely
documented for evaluation by trends analysts.
The introduction of open path methods to the SLAMS monitoring
network may seem relatively straightforward, given the kinds of
technical analyses required in this appendix. However, given the
uncertainties attendant to these analyses and the critical nature and
far-reaching regulatory implications of some sites in the current SLAMS
network composed of point monitors, there is a need to `bridge' between
databases generated by these different candidate methods to evaluate
and promote continuity in understanding of the historical
representativeness of the database.
Concurrent, nominally collocated monitoring must be conducted in
all instances where an open path analyzer is effectively intended to
replace a criteria pollutant point monitor which meets either of the
following:
1. Data collected at the site represents the maximum concentration
for a particular nonattainment area; or
2. Data collected at the site is currently used to characterize the
development of a nonattainment area State implementation plan.
The Regional Administrator, the Administrator, or their appropriate
designee may also require collocated monitoring at other sites which
are, based on historical technical data, significant in assessing air
quality in a particular area. The term of this requirement is
determined by the Regional Administrator (for SLAMS), Administrator
(for NAMS), or their appropriate designee. The recommended minimum term
consists of one year (or one season of maximum pollutant concentration)
with a maximum term indexed to the subject pollutant NAAQS compliance
interval (e.g., three calendar years for ozone). The requirement
involves concurrent monitoring with both the open path analyzer and the
existing point monitor during this term. Concurrent monitoring with
more than one point analyzer with an open path analyzer using one or
more measurement paths may also be advantageous to confirm adequate
peak concentration sensitivity or to optimize the location and length
of the monitoring path or paths.
All or some portion of the above requirement may be waived by the
Regional Administrator (for SLAMS), the Administrator (for NAMS), or
their designee in response to a request, based on accompanying
technical information and analyses, or in certain unavoidable instances
caused by logistical circumstances.
These requirements for concurrent monitoring also generally apply
to situations where the relocation of any SLAMS site, using either a
point monitor or an open path analyzer, within an area is being
contemplated.
* * * * *
6. Appendix E is amended as follows:
a. The heading of appendix E is revised.
b. Section 1 is revised.
c. Section 2 is added and sections 3, 5, and 6 are removed and
reserved.
d. Section 4 is revised.
e. In section 7, table 4 is redesignated as table 3.
f. The first paragraph of section 9 is revised.
g. Section 10 is revised.
h. Section 12 is revised.
Appendix E--Probe and Monitoring Path Siting Criteria for Ambient
Air Quality Monitoring
1. Introduction
This appendix contains specific location criteria applicable to
ambient air quality monitoring probes and monitoring paths after the
general station siting has been selected based on the monitoring
objectives and spatial scale of representation discussed in appendix D
of this part. Adherence to these siting criteria is necessary to ensure
the uniform collection of compatible and comparable air quality data.
The probe and monitoring path siting criteria discussed below must
be followed to the maximum extent possible. It is recognized that there
may be situations where some deviation from the siting criteria may be
necessary. In any such case, the reasons must be thoroughly documented
in a written request for a waiver that describes how and why the
proposed siting deviates from the criteria. This documentation should
help to avoid later questions about the validity of the resulting
monitoring data. Conditions under which the EPA would consider an
application for waiver from these siting criteria are discussed in
section 11 of this appendix.
The spatial scales of representation used in this appendix, i.e.,
micro, middle, neighborhood, urban, and regional, are defined and
discussed in
[[Page 52325]]
appendix D of this part. The pollutant-specific probe and monitoring
path siting criteria generally apply to all spatial scales except where
noted otherwise. Specific siting criteria that are phrased with a
``must'' are defined as requirements and exceptions must be approved
through the waiver provisions. However, siting criteria that are
phrased with a ``should'' are defined as goals to meet for consistency
but are not requirements.
2. Sulfur dioxide (SO2), Ozone (O3), and Nitrogen Dioxide
(NO2)
Open path analyzers may be used to measure SO2, O3, and
NO2 at SLAMS/NAMS sites for middle, neighborhood, urban, and
regional scale measurement applications. Additional information on
SO2, NO2, and O3 monitor siting criteria may be found in
references 11 and 13.
2.1 Horizontal and Vertical Placement
The probe or at least 80 percent of the monitoring path must be
located between 3 and 15 meters above ground level. The probe or at
least 90 percent of the monitoring path must be at least 1 meter
vertically or horizontally away from any supporting structure, walls,
parapets, penthouses, etc., and away from dusty or dirty areas. If the
probe or a significant portion of the monitoring path is located near
the side of a building, then it should be located on the windward side
of the building relative to the prevailing wind direction during the
season of highest concentration potential for the pollutant being
measured.
2.2 Spacing from Minor Sources (Applicable to SO2 and O3
Monitoring Only)
Local minor sources of SO2 can cause inappropriately high
concentrations of SO2 in the vicinity of probes and monitoring
paths for SO2. Similarly, local sources of nitric oxide (NO) and
ozone-reactive hydrocarbons can have a scavenging effect causing
unrepresentatively low concentrations of O3 in the vicinity of
probes and monitoring paths for O3. To minimize these potential
interferences, the probe or at least 90 percent of the monitoring path
must be away from furnace or incineration flues or other minor sources
of SO2 or NO, particularly for open path analyzers because of
their potential for greater exposure over the area covered by the
monitoring path. The separation distance should take into account the
heights of the flues, type of waste or fuel burned, and the sulfur
content of the fuel. It is acceptable, however, to monitor for SO2
near a point source of SO2 when the objective is to assess the
effect of this source on the represented population.
2.3 Spacing From Obstructions
Buildings and other obstacles may possibly scavenge SO2,
O3, or NO2. To avoid this interference, the probe or at least
90 percent of the monitoring path must have unrestricted airflow and be
located away from obstacles so that the distance from the probe or
monitoring path is at least twice the height that the obstacle
protrudes above the probe or monitoring path. Generally, a probe or
monitoring path located near or along a vertical wall is undesirable
because air moving along the wall may be subject to possible removal
mechanisms. A probe must have unrestricted airflow in an arc of at
least 270 degrees around the inlet probe, or 180 degrees if the probe
is on the side of a building. This arc must include the predominant
wind direction for the season of greatest pollutant concentration
potential. A sampling station having a probe located closer to an
obstacle than this criterion allows should be classified as middle
scale rather than neighborhood or urban scale, since the measurements
from such a station would more closely represent the middle scale. A
monitoring path must be clear of all trees, brush, buildings, plumes,
dust, or other optical obstructions, including potential obstructions
that may move due to wind, human activity, growth of vegetation, etc.
Temporary optical obstructions, such as rain, particles, fog, or snow,
should be considered when siting an open path analyzer. Any of these
temporary obstructions that are of sufficient density to obscure the
light beam will affect the ability of the open path analyzer to
continuously measure pollutant concentrations.
Special consideration must be devoted to the use of open path
analyzers due to their inherent potential sensitivity to certain types
of interferences, or optical obstructions. While some of these
potential interferences are comparable to those to which point monitors
are subject, there are additional sources of potential interferences
which are altogether different in character. Transient, but significant
obscuration of especially longer measurement paths could be expected to
occur as a result of certain prevailing meteorological conditions
(e.g., heavy fog, rain, snow) and/or aerosol levels that are of a
sufficient density to prevent the open path analyzer's light
transmission. If certain compensating measures are not otherwise
implemented at the onset of monitoring (e.g., shorter path lengths,
higher light source intensity), data recovery during periods of
greatest primary pollutant potential could be compromised. For
instance, if heavy fog or high particulate levels are coincident with
periods of projected NAAQS-threatening pollutant potential, the
representativeness of the resulting data record in reflecting maximum
pollutant concentrations may be substantially impaired despite the fact
that the site may otherwise exhibit an acceptable, even exceedingly
high overall valid data capture rate.
In seeking EPA approval for inclusion of a site using an open path
analyzer into the formal SLAMS/NAMS or PSD network, monitoring agencies
must submit an analysis which evaluates both obscuration potential for
a proposed path length for the subject area and the effect this
potential is projected to have on the representativeness of the data
record. This analysis should include one or more of the following
elements, as appropriate for the specific circumstance: climatological
information, historical pollutant and aerosol information, modeling
analysis results, and any related special study results.
2.4 Spacing From Trees
Trees can provide surfaces for SO2, O3, or NO2
adsorption or reactions and obstruct wind flow. To reduce this possible
interference, the probe or at least 90 percent of the monitoring path
should be 20 meters or more from the drip line of trees. If a tree or
trees could be considered an obstacle, the probe or 90 percent of the
monitoring path must meet the distance requirements of Section 2.3 and
be at least 10 meters from the drip line of the tree or trees. Since
the scavenging effect of trees is greater for O3 than for other
criteria pollutants, strong consideration of this effect must be given
to locating an O3 probe or monitoring path to avoid this problem.
2.5 Spacing From Roadways (Applicable to O3 and NO2 Only)
In siting an O3 analyzer, it is important to minimize
destructive interferences from sources of NO, since NO readily reacts
with O3. In siting NO2 analyzers for neighborhood and urban
scale monitoring, it is important to minimize interferences from
automotive sources. Table 1 provides the required minimum separation
distances between a roadway and a probe and between a roadway and at
least 90 percent of a monitoring path for various ranges of daily
roadway traffic. A sampling station having a point analyzer probe
located closer to a roadway than allowed by the Table 1 requirements
[[Page 52326]]
should be classified as middle scale rather than neighborhood or urban
scale, since the measurements from such a station would more closely
represent the middle scale. If an open path analyzer is used at a site,
the monitoring path(s) must not cross over a roadway with an average
daily traffic count of 10,000 vehicles per day or more. For those
situations where a monitoring path crosses a roadway with fewer than
10,000 vehicles per day, one must consider the entire segment of the
monitoring path in the area of potential atmospheric interference from
automobile emissions. Therefore, this calculation must include the
length of the monitoring path over the roadway plus any segments of the
monitoring path that lie in the area between the roadway and the
minimum separation distance, as determined from Table 1. The sum of
these distances must not be greater than 10 percent of the total
monitoring path length.
Table 1.--Minimum Separation Distance Between Roadways and Probes or
Monitoring Paths for Monitoring Neighborhood--and Urban--Scale Ozone and
Nitrogen Dioxide
------------------------------------------------------------------------
Minimum
separation
Roadway average daily traffic, vehicles per day distance,\1\
meters
------------------------------------------------------------------------
10,000........................................ 10
15,000................................................. 20
20,000................................................. 30
40,000................................................. 50
70,000................................................. 100
110,000........................................ 250
------------------------------------------------------------------------
\1\ Distance from the edge of the nearest traffic lane. The distance for
intermediate traffic counts should be interpolated from the table
values based on the actual traffic count.
2.6 Cumulative Interferences on a Monitoring Path
The cumulative length or portion of a monitoring path that is
affected by minor sources, obstructions, trees, or roadways must not
exceed 10 percent of the total monitoring path length.
2.7 Maximum Monitoring Path Length
The monitoring path length must not exceed 1 kilometer for
analyzers in neighborhood, urban, or regional scale. For middle scale
monitoring sites, the monitoring path length must not exceed 300
meters. In areas subject to frequent periods of dust, fog, rain, or
snow, consideration should be given to a shortened monitoring path
length to minimize loss of monitoring data due to these temporary
optical obstructions. For certain ambient air monitoring scenarios
using open path analyzers, shorter path lengths may be needed in order
to ensure that the monitoring station meets the objectives and spatial
scales defined for SLAMS in appendix D. Therefore, the Regional
Administrator or the Regional Administrator's designee may require
shorter path lengths, as needed on an individual basis, to ensure that
the SLAMS meet the appendix D requirements. Likewise, the Administrator
or the Administrator's designee may specify the maximum path length
used at monitoring stations designated as NAMS or PAMS as needed on an
individual basis.
* * * * *
4. Carbon Monoxide (CO)
Open path analyzers may be used to measure CO at SLAMS/NAMS sites
for middle or neighborhood scale measurement applications. Additional
information on CO monitor siting criteria may be found in reference 12.
4.1 Horizontal and Vertical Placement
Because of the importance of measuring population exposure to CO
concentrations, air should be sampled at average breathing heights.
However, practical factors require that the inlet probe be higher. The
required height of the inlet probe for CO monitoring is therefore
3\1/2\ meters for a microscale site, which is a compromise
between representative breathing height and prevention of vandalism.
The recommended 1 meter range of heights is also a compromise to some
extent. For consistency and comparability, it would be desirable to
have all inlets at exactly the same height, but practical
considerations often prevent this. Some reasonable range must be
specified and 1 meter provides adequate leeway to meet most
requirements.
For the middle and neighborhood scale stations, the vertical
concentration gradients are not as great as for the microscale station.
This is because the diffusion from roads is greater and the
concentrations would represent larger areas than for the microscale.
Therefore, the probe or at least 80 percent of the monitoring path must
be located between 3 and 15 meters above ground level for middle and
neighborhood scale stations. The probe or at least 90 percent of the
monitoring path must be at least 1 meter vertically or horizontally
away from any supporting structure, walls, parapets, penthouses, etc.,
and away from dusty or dirty areas. If the probe or a significant
portion of the monitoring path is located near the side of a building,
then it should be located on the windward side of the building relative
to both the prevailing wind direction during the season of highest
concentration potential and the location of sources of interest, i.e.,
roadways.
4.2 Spacing from Obstructions
Buildings and other obstacles may restrict airflow around a probe
or monitoring path. To avoid this interference, the probe or at least
90 percent of the monitoring path must have unrestricted airflow and be
located away from obstacles so that the distance from the probe or
monitoring path is at least twice the height that the obstacle
protrudes above the probe or monitoring path. A probe or monitoring
path located near or along a vertical wall is undesirable because air
moving along the wall may be subject to possible removal mechanisms. A
probe must have unrestricted airflow in an arc of at least 270 degrees
around the inlet probe, or 180 degrees if the probe is on the side of a
building. This arc must include the predominant wind direction for the
season of greatest pollutant concentration potential. A monitoring path
must be clear of all trees, brush, buildings, plumes, dust, or other
optical obstructions, including potential obstructions that may move
due to wind, human activity, growth of vegetation, etc. Temporary
optical obstructions, such as rain, particles, fog, or snow, should be
considered when siting an open path analyzer. Any of these temporary
obstructions that are of sufficient density to obscure the light beam
will affect the ability of the open path analyzer to continuously
measure pollutant concentrations.
Special consideration must be devoted to the use of open path
analyzers due to their inherent potential sensitivity to certain types
of interferences, or optical obstructions. While some of these
potential interferences are comparable to those to which point monitors
are subject, there are additional sources of potential interferences
which are altogether different in character. Transient, but significant
obscuration of especially longer measurement paths could be expected to
occur as a result of certain prevailing meteorological conditions
(e.g., heavy fog, rain, snow) and/or aerosol levels that are of a
sufficient density to prevent the open path analyzer's light
transmission. If certain compensating measures are not otherwise
implemented at the onset of monitoring (e.g., shorter path lengths,
higher light source intensity), data recovery during periods of
greatest primary pollutant potential could be compromised. For
instance, if heavy fog or high particulate levels are coincident
[[Page 52327]]
with periods of projected NAAQS-threatening pollutant potential, the
representativeness of the resulting data record in reflecting maximum
pollutant concentrations may be substantially impaired despite the fact
that the site may otherwise exhibit an acceptable, even exceedingly
high overall valid data capture rate.
In seeking EPA approval for inclusion of a site using an open path
analyzer into the formal SLAMS/NAMS or PSD network, monitoring agencies
must submit an analysis which evaluates both obscuration potential for
a proposed path length for the subject area and the effect this
potential is projected to have on the representativeness of the data
record. This analysis should include one or more of the following
elements, as appropriate for the specific circumstance: climatological
information, historical pollutant and aerosol information, modeling
analysis results, and any related special study results.
4.3 Spacing From Roadways
Street canyon and traffic corridor stations (microscale) are
intended to provide a measurement of the influence of the immediate
source on the pollution exposure of the population. In order to provide
some reasonable consistency and comparability in the air quality data
from microscale stations, a minimum distance of 2 meters and a maximum
distance of 10 meters from the edge of the nearest traffic lane must be
maintained for these CO monitoring inlet probes. This should give
consistency to the data, yet still allow flexibility of finding
suitable locations.
Street canyon/corridor (microscale) inlet probes must be located at
least 10 meters from an intersection and preferably at a midblock
location. Midblock locations are preferable to intersection locations
because intersections represent a much smaller portion of downtown
space than do the streets between them. Pedestrian exposure is probably
also greater in street canyon/corridors than at intersections. Also,
the practical difficulty of positioning sampling inlets is less at
midblock locations than at the intersection. However, the final siting
of the monitor must meet the objectives and intent of appendix D,
sections 2.4, 3, 3.3, and appendix E, section 4.
In determining the minimum separation between a neighborhood scale
monitoring station and a specific line source, the presumption is made
that measurements should not be substantially influenced by any one
roadway. Computations were made to determine the separation distance,
and table 2 provides the required minimum separation distance between
roadways and a probe or 90 percent of a monitoring path. Probes or
monitoring paths that are located closer to roads than this criterion
allows should not be classified as a neighborhood scale, since the
measurements from such a station would closely represent the middle
scale. Therefore, stations not meeting this criterion should be
classified as middle scale.
Table 2.--Minimum Separation Distance Between Roadways and Probes or
Monitoring Paths for Monitoring Neighborhood Scale Carbon Monoxide
------------------------------------------------------------------------
Minimum
separation
distance
\1\ for
Roadway average daily traffic, vehicles per day probes or
9012f a
monitoring
path
---------------------------------------------------------------(meters)-
10,000.......................................... 10
15,000................................................... 25
20,000................................................... 45
30,000................................................... 80
40,000................................................... 115
50,000................................................... 135
60,000........................................ 150
------------------------------------------------------------------------
\1\ Distance from the edge of the nearest traffic lane. The distance for
intermediate traffic counts should be interpolated from the table
values based on the actual traffic count.
4.4 Spacing From Trees and Other Considerations
Since CO is relatively nonreactive, the major factor concerning
trees is as obstructions to normal wind flow patterns. For middle and
neighborhood scale stations, trees should not be located between the
major sources of CO, usually vehicles on a heavily traveled road, and
the monitor. The probe or at least 90 percent of the monitoring path
must be 10 meters or more from the drip line of trees which are between
the probe or the monitoring path and the road and which extend at least
5 meters above the probe or monitoring path. For microscale stations,
no trees or shrubs should be located between the probe and the roadway.
4.5 Cumulative Interferences on a Monitoring Path
The cumulative length or portion of a monitoring path that is
affected by obstructions, trees, or roadways must not exceed 10 percent
of the total monitoring path length.
4.6 Maximum Monitoring Path Length
The monitoring path length must not exceed 1 kilometer for
analyzers used for neighborhood scale monitoring applications, or 300
meters for middle scale monitoring applications. In areas subject to
frequent periods of dust, fog, rain, or snow, consideration should be
given to a shortened monitoring path length to minimize loss of
monitoring data due to these temporary optical obstructions. For
certain ambient air monitoring scenarios using open path analyzers,
shorter path lengths may be needed in order to ensure that the
monitoring station meets the objectives and spatial scales defined for
SLAMS in appendix D. Therefore, the Regional Administrator or the
Regional Administrator's designee may require shorter path lengths, as
needed on an individual basis, to ensure that the SLAMS meet the
appendix D requirements. Likewise, the Administrator or the
Administrator's designee may specify the maximum path length used at
monitoring stations designated as NAMS or PAMS as needed on an
individual basis.
* * * * *
Table 3--Separation Distance Between Pb Stations and Roadways (Edge of
Nearest Traffic Lane)
* * * * *
9. Probe Material and Pollutant Sample Residence Time
For the reactive gases, SO2, NO2, and O3, special
probe material must be used for point analyzers. Studies20-24 have
been conducted to determine the suitability of materials such as
polypropylene, polyethylene, polyvinyl chloride, Tygon, aluminum,
brass, stainless steel, copper, Pyrex glass and Teflon for use as
intake sampling lines. Of the above materials, only Pyrex glass and
Teflon have been found to be acceptable for use as intake sampling
lines for all the reactive gaseous pollutants. Furthermore, the
EPA25 has specified borosilicate glass or FEP Teflon as the only
acceptable probe materials for delivering test atmospheres in the
determination of reference or equivalent methods. Therefore,
borosilicate glass, FEP Teflon, or their equivalent must be used for
existing and new NAMS or SLAMS.
* * * * *
10. Photochemical Assessment Monitoring Stations (PAMS)
10.1 Horizontal and Vertical Placement
The probe or at least 80 percent of the monitoring path must be
located 3 to 15
[[Page 52328]]
meters above ground level. This range provides a practical compromise
for finding suitable sites for the multipollutant PAMS. The probe or at
least 90 percent of the monitoring path must be at least 1 meter
vertically or horizontally away from any supporting structure, walls,
parapets, penthouses, etc., and away from dusty or dirty areas.
10.2 Spacing From Obstructions
The probe or at least 90 percent of the monitoring path must be
located away from obstacles and buildings such that the distance
between the obstacles and the probe or the monitoring path is at least
twice the height that the obstacle protrudes above the probe or
monitoring path. There must be unrestricted airflow in an arc of at
least 270 deg. around the probe inlet. Additionally, the predominant
wind direction for the period of greatest pollutant concentration (as
described for each site in section 4.2 of appendix D) must be included
in the 270 deg. arc. If the probe is located on the side of the
building, 180 deg. clearance is required. A monitoring path must be
clear of all trees, brush, buildings, plumes, dust, or other optical
obstructions, including potential obstructions that may move due to
wind, human activity, growth of vegetation, etc. Temporary optical
obstructions, such as rain, particles, fog, or snow, should be
considered when siting an open path analyzer. Any of these temporary
obstructions that are of sufficient density to obscure the light beam
will affect the ability of the open path analyzer to continuously
measure pollutant concentrations.
Special consideration must be devoted to the use of open path
analyzers due to their inherent potential sensitivity to certain types
of interferences, or optical obstructions. While some of these
potential interferences are comparable to those to which point monitors
are subject, there are additional sources of potential interferences
which are altogether different in character. Transient, but significant
obscuration of especially longer measurement paths could be expected to
occur as a result of certain prevailing meteorological conditions
(e.g., heavy fog, rain, snow) and/or aerosol levels that are of a
sufficient density to prevent the open path analyzer's light
transmission. If certain compensating measures are not otherwise
implemented at the onset of monitoring (e.g., shorter path lengths,
higher light source intensity), data recovery during periods of
greatest primary pollutant potential could be compromised. For
instance, if heavy fog or high particulate levels are coincident with
periods of projected NAAQS-threatening pollutant potential, the
representativeness of the resulting data record in reflecting maximum
pollutant concentrations may be substantially impaired despite the fact
that the site may otherwise exhibit an acceptable, even exceedingly
high overall valid data capture rate.
In seeking EPA approval for inclusion of a site using an open path
analyzer into the formal SLAMS/NAMS or PSD network, monitoring agencies
must submit an analysis which evaluates both obscuration potential for
a proposed path length for the subject area and the effect this
potential is projected to have on the representativeness of the data
record. This analysis should include one or more of the following
elements, as appropriate for the specific circumstance: climatological
information, historical pollutant and aerosol information, modeling
analysis results, and any related special study results.
10.3 Spacing From Roadways
It is important in the probe and monitoring path siting process to
minimize destructive interferences from sources of NO since NO readily
reacts with O3. Table 4 below provides the required minimum
separation distances between roadways and PAMS (excluding upper air
measuring stations):
Table 4.--Separation Distance Between Pams and Roadways
[Edge of Nearest Traffic Lane]
------------------------------------------------------------------------
Minimum
separation
distance
between
Roadway average daily traffic, vehicles per day roadways
and
stations in
meters \1\
------------------------------------------------------------------------
<10,000................................................... >10
15,000.................................................... 20
20,000.................................................... 30
40,000.................................................... 50
70,000.................................................... 100
>110,000.................................................. 250
------------------------------------------------------------------------
\1\ Distance from the edge of the nearest traffic lane. The distance for
intermediate traffic counts should be interpolated from the table
based on the actual traffic flow.
10.4 Spacing From Trees
Trees can provide surfaces for adsorption and/or reactions to occur
and can obstruct normal wind flow patterns. To minimize these effects
at PAMS, the probe or at least 90 percent of the monitoring path should
be placed at least 20 meters from the drip line of trees. Since the
scavenging effect of trees is greater for O3 than for the other
criteria pollutants, strong consideration of this effect must be given
in locating the PAMS probe or monitoring path to avoid this problem.
Therefore, the probe or at least 90 percent of the monitoring path must
be at least 10 meters from the drip line of trees.
* * * * *
12. Summary
Table 5 presents a summary of the general requirements for probe
and monitoring path siting criteria with respect to distances and
heights. It is apparent from Table 5 that different elevation distances
above the ground are shown for the various pollutants. The discussion
in the text for each of the pollutants described reasons for elevating
the monitor, probe, or monitoring path. The differences in the
specified range of heights are based on the vertical concentration
gradients. For CO, the gradients in the vertical direction are very
large for the microscale, so a small range of heights has been used.
The upper limit of 15 meters was specified for consistency between
pollutants and to allow the use of a single manifold or monitoring path
for monitoring more than one pollutant.
[[Page 52329]]
Table 5.--Summary of Probe and Monitoring Path Siting Criteria
----------------------------------------------------------------------------------------------------------------
Horizontal and
Height from vertical distance
Scale [maximum ground to probe from supporting Distance from Distance from
Pollutant monitoring path or 8012f structures B to trees to probe or roadways to probe
length, meters] monitoring path A probe or 9012f 90212f monitoring or monitoring
(meters) monitoring path A path A (meters) path A (meters)
(meters)
----------------------------------------------------------------------------------------------------------------
SO2 C,D,E,F...... Middle [300m] 3-15............. >1............... >10.............. N/A.
Neighborhood,
Urban, and
Regional [1km].
CO D,E,G......... Micro Middle 30.5; >1............... >10.............. 2-10; See Table 2
[300m] 3-15. for middle and
Neighborhood neighborhood
[1km]. scales.
O3 C,D,E......... Middle [300m] 3-15............. >1............... >10.............. See Table 1 for
Neighborhood, all scales.
Urban, and
Regional [1km].
Ozone precursors Neighborhood and 3-15............. >1............... >10.............. See Table 4 for
(for PAMS) C,D,E. Urban. all scales.
[1 km]...........
NO2 C,D,E........ Middle [300m] 3-15............. >1............... >10.............. See Table 1 for
Neighborhood and all scales.
Urban [1km].
Pb C,D,E,F,H..... Micro; Middle, 2-7 (Micro); 2-15 >2 (All scales, >10 (All scales). 5-15 (Micro); See
Neighborhood, (All other horizontal Table 3 for all
Urban and scales). distance only). other scales.
Regional.
PM-10 C,D,E,F,H.. Micro; Middle, 2-7 (Micro); 2-15 >2 (All scales, >10 (All scales). 2-10 (Micro); See
Neighborhood, (All other horizontal Figure 2 for all
Urban and scales). distance only). other scales.
Regional.
----------------------------------------------------------------------------------------------------------------
N/A--Not applicable.
A Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring and
all applicable scales for monitoring SO2, O3, O3 precursors, and NO2.
B When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses
located on roof.
C Should be >20 meters from the dripline of tree(s) and must be 10 meters from the dripline when the tree(s) act
as an obstruction.
D Distance from sampler, probe, or 9012f monitoring path to obstacle, such as a building, must be at least
twice the height the obstacle protrudes above the sampler, probe, or monitoring path. Sites not meeting this
criterion may be classified as middle scale (see text).
E Must have unrestricted airflow 270 deg. around the probe or sampler; 180 deg. if the probe is on the side of a
building.
F The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration
flues. The separation distance is dependent on the height of the minor source's emission point (such as a
flue), the type of fuel or waste burned, and the quality of the fuel (sulfur, ash, or lead content). This
criterion is designed to avoid undue influences from minor sources.
G For microscale CO monitoring sites, the probe must be >10 meters from a street intersection and preferably at
a midblock location.
H For collocated Pb and PM-10 samplers, a 2-4 meter separation distance between collocated samplers must be met.
* * * * *
[FR Doc. 95-24042 Filed 10-5-95; 8:45 am]
BILLING CODE 6560-50-P