REGULATORY MONITORING STRATEGY FOR A REVISED PM NAAQS

A Blueprint for a New National Monitoring Program for Particulate Matter

Neil H. Frank

USEPA

Office of Air Quality Planning and Standards

Research Triangle Park, NC 27711

GLOSSARY OF TERMS	3

KEY CHANGES TO A NEW PM MONITORING PROGRAM	4

1.0 INTRODUCTION	5

2.0 STATE AIR QUALITY SURVEILLANCE SYSTEM FOR PM	6

2.1 PM-10 Sites	6

2.2 PM-fine Sites	7

2.2.1 Core SLAMS Network	7

2.2.2 PM-fine NAMS	9

2.2.3 Other PM-fine SLAMS sites	9

2.2.4 Special Purpose Monitors	9

3.0 A BLUEPRINT FOR PM MONITORING	10

3.1 The State PM Monitoring Plan	10

3.2 Monitoring Planning Areas	10

3.2.1 Monitoring within an MPA	11

3.3 Other State Monitoring Requirements	12

3.4 Siting of New PM-fine Monitors	13

3.5 Optional Monitoring	13

3.6 Exceptions to PM-fine Monitoring Requirements	14

4.0 NATIONAL AIR MONITORING STATIONS	14

5.0 ANNUAL PM SURVEILLANCE REVIEW AND REPORTING	16

5.1 Data Reporting	17

6.0 NETWORK COMPLETION SCHEDULES	17

6.1 SLAMS Networks	17

6.2 NAMS Networks	18

Table 1. Types of PM Networks	19

Table 2. Size of Air Surveillance Monitoring Networks (1994)	20

Table 3. Proposed PM-fine NAMS by EPA Region (Goals)	21

GLOSSARY OF TERMS

SLAMS	State and Local Air Monitoring Stations

Core SLAMS	SLAMS which are required to sample everyday

NAMS	SLAMS which are intended for long term trends

SPMs	Special Purpose Monitors

Category "a" site	Core SLAMS (or NAMS) population-oriented site located in area of expected maximum concentration

Category "b" site	Core site located in area of poor air quality with maximum population impact.

NAAQS	National Ambient Air Quality Standard

FRM	Federal Reference Method,

i.e. measurement method for a NAAQS pollutant meeting requirements of 40 CFR 50 and 40 CFR 53

REM	Reference or equivalent method, i.e. FRM or equivalent method according to 40 CFR 53

MPA	Monitoring Planning Area

SIP	State Implementation Plan

KEY CHANGES TO A NEW PM MONITORING PROGRAM

A sequential, semi-automatic PM-fine sampling method would provide up to four integrated 24-
hour gravimetric measurements with a single visit by the site operator (Section 1.0)

Downsizing of existing PM-10 networks (Section 2.1)

Tiered PM-fine monitoring networks which require the most complete information at population-
oriented "Core" sites and flexibility in data collection at other locations. (Section 2.2)

Require daily sampling of PM-fine at the Core sites which would be representative of typical community-wide exposure (Section 2.2.1)

For PM-fine, middle or neighborhood spatial scales would be most appropriate to represent typical community-wide exposure (Section 2.2.1)

State Monitoring Plan and designated monitoring areas to provide flexibility to the States in implementing new monitoring regulations (Section 3.1, 3.2)

Require specific numbers of population-oriented monitors throughout the nation in the areas of expected maximum concentration and in areas of more typical poor air quality (Section 3.2.1)

Require background and regional transport sites with daily sampling (Section 3.3)

Require archival of filters to provide the capability for future compositional analyses (Section 3.3)

Collocate new PM-fine at some sites currently collecting ozone precursor data to establish linkages to ozone program and to assist the understanding of secondarily formed particles (Section 3.2, 3.4)

Permit mass measurements produced at existing IMPROVE sites to represent background concentrations in the new PM-fine network (Section 3.4)

Encourage, but not required, compositional analysis of filters, meteorological measurements, use of supplementary continuous fine particle analyzers and non-reference pollutant measurements to provide adequate PM characterization needed to support implementation program.(Section 3.5)

PM-fine network for trends and other national analyses would be derived from the Core sites. The network would cover the cross section of PM-fine population-oriented monitoring situations for each Region of the country (Section 4.0)

State monitoring report and plan revisions submitted to EPA for annual review to ensure a dynamic network with appropriate Federal oversight (Section 5.0)

3-year phase-in for new PM-fine monitoring network (Section 6.1, 6.2)

1.0 INTRODUCTION

This paper provides staff recommendations for new ambient air surveillance regulatory requirements for particulate matter. Nationwide monitoring would be performed for two indicators of particulate matter: PM-10 and fine particulate, PM-fine (e.g. PM-2.5). It is assumed that an annual National Ambient Air Quality Standard (NAAQS) for PM-10 would be retained and a new annual and 24-hour NAAQS would be established for PM-fine. Current manual and continuous PM-10 sampling equipment that are reference or equivalent could be continued in new PM-10 monitoring networks and a new PM-fine Federal Reference Method (FRM) would be established. A sequential, semi-automatic PM-fine sampling method would provide up to four integrated 24-hour gravimetric measurements with a single visit by the site operator. This would facilitate a new requirement for daily PM-fine sampling. Equivalent manual or continuous analyzers could be approved for network use, provided that they adhere to established performance and field test requirements. Network measurements with all samplers will be subjected to new stringent quality assurance procedures to assure acceptable precision and comparability to a standard FRM device. This will ensure consistency and stability in the national network and provide a basis for a fair and equitable implementation program.

The new air surveillance regulations (40 CFR 58) would establish a monitoring program whose primary purpose is determination of NAAQS attainment/nonattainment and whose primary emphasis is population-oriented surveillance. The program would involve different types of monitoring sites which would provide flexibility to the States to collect needed information, reduce or eliminate unnecessary information, and conserve costs. (See Table 1 for an overview of new PM networks and a glossary of terms). The major focus would be placed on collecting the most complete (i.e. daily) information in heavily populated areas where likelihood of exposure is high. Less complete information would be allowed in less densely populated areas or to provide necessary spatial resolution. Air quality data regarding regional background and transport would also be collected to assist the implementation program. The new monitoring network requirements would become effective 6 months after the date of NAAQS promulgation to allow time for procurement of new samplers and the new networks would be phased in over three years in a prioritized fashion to make use of limited monitoring resources. The initial priority for new monitors would be areas with the large populations that are likely to be exposed to elevated PM levels.

2.0 STATE AIR QUALITY SURVEILLANCE SYSTEM FOR PM

Air quality surveillance networks consist of State and Local Air Monitoring Stations (SLAMS), National Air Monitoring Stations (NAMS), Photochemical Assessment Monitoring Stations (PAMS), Special Purpose Monitors (SPMs). The SLAMS is the ambient air monitoring network which is required by EPA regulation to provide ambient concentrations of pollutants for which NAAQS have been established. All SLAMS data receive Federal funding and must be submitted to EPA. There are two special subsets of the SLAMS, each with separate regulatory requirement. First are the NAMS which are intended for national trends and policy analyses. Second are the PAMS, required in the 22 generally high population areas which have the nation's worst ozone air quality problem to monitor for ozone and its precursor pollutants. Each network has individual requirements for number and location of sites, for frequency of monitoring and quality assurance.1 In addition to these regulatory networks, SPMs are deployed by the States to supplement the SLAMS networks. With a revised PM monitoring program, each pollutant indicator (PM-10, PM-fine) would have separate SLAMS, NAMS, SPM networks. The use of these networks for PM monitoring is discussed in the remainder of Section 2.

2.1 PM-10 Sites

The new network for PM-10 would be derived from the existing network of NAMS, SLAMS and SPMs. The current network size for PM-10 and other pollutants is shown in Table 2. With a revised regulation, the population-oriented NAMS would generally be maintained and other key sampling locations in existing nonattainment areas would be continued. The currently approved reference or equivalent PM-10 samplers could continue to be utilized. The revised network would ensure that analysis of national trends in PM-10 can be continued and that air surveillance in areas with established PM emission control programs can be maintained. PM-10 should be collocated with new PM-fine sites at key population oriented monitoring stations so that better definition of fine and coarse contributions to total PM can be determined for a better understanding of exposure, emission controls and atmospheric processes. Most other PM-10 monitoring sites should be discontinued and in fact would be discouraged in a longer term PM-10 network. Until the a new PM-fine is fully configured, however, PM-10 sites could serve as a surrogate for PM-fine and could be continued in areas where high PM-fine levels are suspected.

If the 24-hour PM-10 NAAQS is eliminated, the sampling frequency at all PM-10 sites should be reduced to once in 6 days. This would be sufficient to estimate an annual average concentration. The current monitoring regulation requires every day or every other day sampling for PM-10 at certain sites (i.e. when the site is close to the 24-hr NAAQS). However, less than 20 percent of the PM-10 sites sample more often than once in 6 days. Despite current requirements, this result is attributed to the difficulties and expense associated with frequent sampling for PM-10 and to the recognized relative bias between manual and continuous PM-10 methods. The proposed combination of fewer PM-10 sites and reduction in required sampling frequency would save significant resources that could be redirected to fine particle monitoring.

2.2 PM-fine Sites

A new network for PM-fine would consist of a "Core" network of population-oriented SLAMS monitors, "Core" background and transport sites, a NAMS subset for long-term monitoring, other SLAMS monitors and a supplementary network of Special Purpose Monitors. The new network will be based, in part, on a required number of SLAMS. However, the mature national network would be expected to include many more SLAMS in addition to those required by new regulations and would also need many SPMs. To satisfy these goals, sufficient resources must be allocated for the establishment and operation of the national network. A summary of monitoring objectives, allowable measurement method and required frequency of sampling is shown in Table 1.

The design of Core SLAMS, NAMS and other networks will each be discussed in a separate section below. For now, it suffices to say that many of the new PM-fine sites are expected to be located at existing PM-10 monitoring locations and some would be located at PAMS sites.

2.2.1 Core SLAMS Network. The new Core monitoring locations would be an important part of the basic PM-fine SLAMS regulatory network. These sites are intended to primarily reflect community-wide air pollution, which would be consistent with the averaging time of the NAAQS. For a 24-hour or annual PM-fine NAAQS, monitoring locations in residential areas or where people spend a substantial part of the day take precedence over locations with transient populations. Special consideration should also be given to potential exposure by sensitive populations within the monitoring area. In addition to the population- oriented monitoring sites, Core monitors would also be established for background and transport monitoring. Because Core monitors are part of the basic SLAMS regulatory network, reference or equivalent methods (REM) would be required.

The new Core population-oriented PM-fine network is conceptually similar to the existing NAMS for other pollutants, but would allow for some year to year changes in site location to ensure that the typical areas of high pollution, high population areas are always monitored. A certain number of Core sites will be required by regulation to ensure protection of the general population. Core sites will be the key sampling locations designated for initial monitoring, and a subset would be selected for longer-term monitoring. The latter would become the NAMS.

The Core sites will also produce the most complete data in the PM-fine network. Daily sampling would be required, except during low pollution seasons or other periods as exempted by EPA. As such, a subset of these sites should be considered as candidate locations for adding state-of-the-art research monitoring devices whose data might need to be considered in future reviews of the PM NAAQS. This will ensure continuity and comparability of past, present and future PM data bases.

Finally, because the Core sites would produce the most data, many would be the most likely locations for determining violations of a short-term NAAQS. The Core locations would become critical for judging future attainment in an area that has been determined to violate the NAAQS, again putting emphasis on areas with the largest population impact. Complete data at background and transport Core sites will also provide the needed data base to better understand the source-receptor relationships and assist the implementation program.

Scales of representativeness are used to describe the approximate zone of spatially homogeneous ambient air in the vicinity of a monitoring location. Described scales are: micro (< 100m), middle (100m - 0.5km), neighborhood (0.5-4km), urban (4-50km) , regional (10's - 100's of km) and national/global. In general, population-oriented Core sites should be located near inhabited buildings or locations representative of where the general public can be expected to be exposed to the concentration measurement.2 For PM-fine, middle or neighborhood spatial scales would be most appropriate to represent typical community-wide exposure. These would be preferable for the new population-oriented Core sites. This is a departure from the current regulations which encourage PM monitoring in micro scale locations. With a revised monitoring regulation, all locations in the ambient air would still be permissible in a new SLAMS network.3 However, micro scale locations which reflect specific mobile or stationary source impacts would be allowed for a Core site if and only if this site was representative of many such micro environments within a monitoring area.

2.2.2 PM-fine NAMS. The PM-fine NAMS would be a subset of the Core network and are intended to establish national trends and provide a data base for future regulatory and policy analyses. As Core sites, NAMS would also use REM measurement methods and sample everyday. Approximately 250 sites are anticipated in the mature PM-fine NAMS network. The design of the NAMS network is discussed in a section below.

2.2.3 Other PM-fine SLAMS sites. In addition to a specified number of Core sites which would be required by the regulation, other SLAMS sites would be needed in a State air surveillance program. These additional sites may be located anywhere in the ambient air, but preference should be given to population-oriented locations even for those sites which record the maximum concentrations. The selection of these population-oriented locations should not be restricted however, by population density or total population magnitude. Higher priority could be assigned to residential areas (e.g., especially areas near hospitals, schools, retirement homes), as opposed to industrial districts where people do not live and sensitive populations do not spend a lot of time.

These non-Core SLAMS sites would not be required to sample every day. In general, these sites would sample a minimum of once in 6 days, but episodic or seasonal sampling could also be possible (e.g. in areas where significant violations of the 24-hr NAAQS are expected), or at sites heavily influenced by regional transport. Because incomplete sampling would be allowed at this subset of the SLAMS network, the rules for interpreting status with respect to the NAAQS should not impose penalties to sites that provide the required data capture (i.e. observed data should not be extrapolated to estimate results derived from everyday sampling). This would encourage the collection of additional data without the fear that it would unfairly cause an area to become nonattainment with the NAAQS.

The number of such non-Core SLAMS would be proposed by the State and reviewed by EPA. These sites would monitor according to five monitoring objectives: the traditional SLAMS monitoring objectives (maximum concentration, population exposure, source-oriented monitoring, background) and could also monitor for regional transport. When such supplementary SLAMS regulatory monitors are sited in areas of maximum concentration, population-oriented surveillance is still preferred.

2.2.4 Special Purpose Monitors. Special purpose monitoring would be needed to assist with initial problem identification, to help define boundaries of problem areas, to better define temporal (e.g. diurnal ) patterns, to determine micro scale locations of extreme concentration and to help characterize chemical composition of PM (using alternative samplers), especially on high concentration days or during special studies. SPMs are an important part of the overall PM monitoring program and sufficient resources must be allocated for their use.

SPMs may sample with any measurement method on any sampling schedule. In fact, use of a variety of measurement methods are anticipated to supplement or supplant the Federal Reference Method. Simple inexpensive portable devices or more sophisticated equipment may be used. The latter alternative methods may be needed to provide a more complete characterization of the ambient aerosol. The data from such monitors would not be used for attainment or nonattainment assessment if the monitoring method was not REM. Moreover, in order to encourage the deployment of SPMs during the first few years of PM-fine data collection (e.g., 1 to 2 years following promulgation of Part 58), the monitoring regulations would indicate that nonattainment designations would not be based on REM data produced at an SPM site. This temporary moratorium on use of data collected by SPMs would also be addressed in the advanced notice for proposed rule making (ANPR) for the particulate matter implementation program. However, a notice of NAAQS violations resulting from SPMs should be reported to EPA (as per Section 5.0) and be considered by the State in the design of its overall SLAMS network.

3.0 A BLUEPRINT FOR PM MONITORING

3.1 The State PM Monitoring Plan

Each State shall detail its PM monitoring program in a plan which would be submitted to EPA for its review and approval. The initial plan would be submitted to EPA within 6 months of promulgation of the new monitoring rules. The plan would describe the PM monitoring strategy based on the use of SLAMS (including Core monitors and NAMS) and SPM monitors for PM-fine and PM-10. This includes the phase-in of new PM-fine monitoring sites and changes to the existing PM-10 monitoring program. The plan would also describe the monitoring objectives and scale of representativeness to facilitate subsequent interpretation of measurement data. This would also notify EPA about SPM monitoring objectives and data that are intended for regulatory purposes. Proposed deviations from the general sampling frequency requirements would also be presented for consideration.

A key component of a State's initial monitoring plan is the proposal of Monitoring Planning Areas (MPAs) within which the State's monitoring networks would be derived. The MPAs will determine the number of required Core monitors for the State and specify other SLAMS and SPMs as needed.

3.2 Monitoring Planning Areas

Each State should divide itself into MPAs, from one to approximately 25 in number. A small or low population State like Rhode Island may only have one State-wide MPA, while a State like California might have 25. The number of MPAs will depend on total population, number of metropolitan areas, topography and PM emission information such as the number and type of significant PM sources.

The MPAs would include the largest metropolitan areas in the country. For each State, this would include all medium-large metropolitan statistical areas (MSA)4, with populations generally greater than 0.5 million. They would also include medium sized metropolitan areas (population between 0.25 and 0.5 million) in which PM-fine concentrations are expected to exceed the PM-fine NAAQS. For example, these could be based on all medium metropolitan areas within which the PM-10 annual average concentration is greater than X ug/m3. As indicated above, the MPAs may be based on air quality planning districts or other air pollution basins in the State. In addition, a portion of a State that is designated nonattainment with the PM NAAQS must correspond to one or more MPAs.

The MPAs should generally not have less than 0.25 million and not more than 2 million population. If the MPAs do not cover the entire State, the remaining portion of the State should be considered as a separate monitoring area. This will ensure that the population of the entire country are covered by a reasonable number of MPAs. Core monitors will not be required in this latter monitoring area and instead, different SLAMS requirements will apply (as discussed in Section 3.3).

3.2.1 Monitoring within an MPA. At least two population-oriented Core PM-
fine SLAMS sites are required in each MPA. At least one site would be situated in the area of expected maximum concentration, analogous to NAMS "category a."5 This will henceforth be termed a category a Core SLAMS site. At least one additional site would be located in the area of poor air quality with high population density or representative of maximum population impact, analogous to NAMS, "category b." 6 This second site will be called a category b Core SLAMS site. A conceptual picture of the location of monitors with respect to population and pollution zones is depicted in Figure 1. Those MPAs which are substantially impacted by several different local sources of fine particles should have separate Core sites to monitor each influencing source region.

For those MPAs that correspond to PAMS areas, at least 3 population-oriented Core PM-fine SLAMS sites would be required, with at least one site collocated with an existing PAMS site. This will permit concomitant measurements of PM-fine and ozone precursors. Finally, for all MSAs with more than 1 million people, a continuous PM analyzer or nephelometer must be used at the categoy b PM-fine Core SLAMS site. This minimum requirement will facilitate daily reporting of an air quality index to the general public.

PM-10 sampling should be performed at the new Core PM-fine sites. If existing PM- 10 monitoring sites are selected, once in 6-day PM-10 sampling should be continued. It must be noted, however, that the most appropriate location for a new PM-fine Core sampling location may not be an existing PM-10 site. In this event, PM-10 sampling should be added, if possible. The prior existence of PM-10 SLAMS or even NAMS monitoring should not be used as a primary criterion for selecting the location of new PM-fine Core sampling.

3.3 Other State Monitoring Requirements

Each State would also be required to have at least one Regional background Core PM- fine SLAMS monitor per State and at least one Regional transport Core PM-fine SLAMS monitor per State. A simple schematic of background and transport monitoring is illustrated in Figure 2.

In addition, one other SLAMS site (non-Core) would be required for each 0.25 million population. A hypothetical diagram of these requirements are shown in Figure 3 together with a numerical example of the total network sites. Background Core monitoring sites may be located in an adjacent State with similar air quality. Also, the regional transport and background Core site may be satisfied by one location or may be exempted by EPA where needs for such data is not warranted. Such would be the case if Core population oriented site is shown to not have a substantial contribution (e.g. 20 percent) from regional sources.

To facilitate future compositional analysis, the State would be expected to archive all collected filters in a proper storage facility. The time duration for the archive would be a period of not less than 1 year for all sites and a period of 3 to 5 or more years for NAMS sites. The former would assist data validation, interpretation of high pollution days and the development of control strategies. The latter would provide the future capability to perform special analyses or develop national trends in specific chemical components.

3.4 Siting of New PM-fine Monitors

The design of new NAMS and SLAMS PM-fine networks would be based on an evaluation of emission inventories, emission density, modeling and the existing PM-10 networks. Potential site locations to be considered include but are not limited to: high concentration PM-10 SLAMS sites, existing PM-10 NAMS sites (for candidate Core population locations), PAMS sites (for transport and other Core locations), and IMPROVE7 sites (for regional background). Potential monitoring at PAMS sites should consider existing PAMS site type 2 (area of highest concentration of ozone precursor ambient concentrations) and site type 3 (location of highest downwind ozone). New setback distances from roadways and other influences are under consideration to ensure that new PM-fine measurements capture particles from the fine mode of the particle distribution with minimal contributions from the coarse mode. It is noted that existing PM-fine IMPROVE monitoring equipment8 would be used to continue to provide PM-fine concentration measurements, although the frequency must coincide with the new daily sampling requirement for total mass. Guidance would be developed to further refine criteria for the siting of new PM-fine monitoring stations.

3.5 Optional Monitoring

In addition to the requirements described above, other monitoring may be necessary and is expected to be part of the overall monitoring program.

Because the reference method would only require the integrated measurement of total mass for a 24-hour period (for subsequent compositional analysis, as necessary), it is recommended that supplementary continuous instrumentation (e.g. TEOM or nephelometer) be deployed at all key population oriented monitoring locations to establish time resolved information. These sites would include category b Core monitors which are representative of typical population exposure. Continuous PM-fine measurements could be provided by equivalent PM-fine analyzers, if equivalency of such equipment is established. Hourly or higher temporal information could be very useful for understanding the sources or atmospheric behavior of fine particle, is important for daily reporting of the Pollutant Standards Index and is especially useful for public notification during air pollution episodes.

Other PM-fine SLAMS and SPM monitoring sites should also be utilized as needed. For example, in areas with known or suspected influence by long-term transport, additional sites for this purpose should be utilized. Local ground level meteorological measurements are also recommended, especially at Core PM-fine population-oriented and transport site SLAMS sites. Use of non-reference measurements (e.g. using denuders or different filter media) would also be needed to develop better characterization of the PM aerosol. Meteorological and alternative concentration measurements are useful to assist in the interpretation of data and understanding of contributing sources. Guidance would be needed to relate reference and non- reference measurements to ensure that data are interpreted consistently for source apportionment and other implementation purposes.

3.6 Exceptions to PM-fine Monitoring Requirements

In order to provide flexibility in new monitoring requirements so that unnecessary information would not be produced, the regulations would permit a variety of exceptions approvable by EPA.

First, within each monitoring planning area, one Core monitor may be exempted by the Regional Administrator. This may be appropriate in areas where the highest concentration is expected to occur at the same location as the area of maximum or sensitive population impact, or areas with low concentrations (e.g. highest concentrations are less than 80 percent of the NAAQS). For the latter areas, the category b monitor is preferred. Second, PM-10 monitoring may be used as an official surrogate for required PM-fine, if historical PM-10 is less than the levels of the PM-fine NAAQS or until new PM-fine monitors are deployed in the system. If PM-10 is used as an official surrogate for PM-fine, then 1 year of parallel sampling following the addition of PM-fine monitoring would be required. Next, sampling frequency at Core sites may be reduced to once in 6 days during seasons or periods of low PM-fine. This would have to be demonstrated with actual PM-fine data, following 1 or more years of PM- fine sampling. Finally, year round sampling may be replaced with episodic sampling at sites which produce the highest concentrations relative to the 24-hr NAAQS.

4.0 NATIONAL AIR MONITORING STATIONS

The NAMS sites have traditionally been long-term monitoring sites which represent maximum pollutant concentration and areas of poor air quality with a high population density. Emphasis has been given to urban and multi-source areas. The existing NAMS for PM-10 satisfy these objectives and should continue in operation. With the revision to the PM NAAQS, it is proposed that new PM-fine NAMS sites be established to provide nationwide geographic coverage and characterize the diversity of emission sources contributing to high PM-fine concentrations in populated areas. The new network should also include sites to represent multi-State transport affecting metropolitan populations.

The PM-fine network should be designed to provide sufficient data on which to perform national and regional trends as well as policy analyses. To satisfy these objectives, approximately 250 PM-fine NAMS sites should be established. These sites would be selected from the Core SLAMS described earlier. Instead of specifying a national number, a target range of 200 to 300 sites shall be utilized. These numbers are comparable to the current number of NAMS sites for both PM-10 and O3. It should be noted that the new PM-fine network may only have a subset of its sites in common with the existing PM-10 network.

Currently, areas within which NAMS sites are located are determined by urbanized population and PM-10 pollutant concentration levels. All urban areas with population greater than 500,000 currently are required to have one to ten PM-10 NAMS and smaller areas, with population of 100,000 to 500,000 have from zero to four monitors. There are 317 PM-10 NAMS sites.9

For the new PM-fine NAMS network, a more flexible approach is proposed. First, metropolitan statistical areas instead of urban areas would be used to identify population centers. Second, a specific number of NAMS sites would only be required for the largest metropolitan areas: two NAMS sites would be required for the approximately 50 MSAs with population greater than 1 million. These sites will be selected to represent maximum population exposures to the dominant sources of emissions causing high ambient PM-fine concentration in the metropolitan area. Finally, to represent the remaining metropolitan portions of each EPA Region, specific numbers of sites will not be specified for each individual MSA. Instead, a range of total NAMS sites per EPA Region would be proposed to cover the cross section of PM-fine monitoring situations where the pollutant concentration and the population exposure are expected to be the highest consistent with the averaging time of the NAAQS for that Region. Such NAMS sites would, in most cases, be neighborhood scale and should be selected from the category b Core monitors which reflect maximum population impact.

Because of the more spatially homogeneous nature of fine particles, the long-range transport phenomenon would also be represented in the PM-fine NAMS monitoring network and one to three transport PM-fine sites would be required per EPA Region to help track the influences that affect downwind metropolitan areas. These transport sites are expected to be more regional in scale. The final number of total PM-fine NAMS sites per Region would be based on recommendations by the EPA Regional Offices, in concert with their State and local agencies.

The selected sites should represent the range of conditions (site types) occurring in the Regions (e.g. urban mix; mobile sources, maybe specific categories, such as diesel, heavy duty vehicle; industrial complex; regional transport; residential wood smoke; and other categories that may be warranted). Furthermore, to reduce redundancy in information across similar areas, not all metropolitan areas with population less than one million must have a NAMS monitor. For example, an urban mix or regional transport site in or near Allentown, PA may provide similar information to one in Harrisburg; both have 500,000 people. With this flexible approach, NAMS data may then be aggregated according to site type, in order to perform a variety of regional and national trend and other analyses.

Although the approach is not intended to be prescriptive, a relative number of monitors per Region is nevertheless needed to ensure geographic balance in the national network. Table 3 presents the desired number of monitors per Region. These numbers consider a variety of factors such as Regional differences in metropolitan population, population density, land area, PM emission sources and existing numbers of PM-10 NAMS sites.

Since PM-fine would be a new monitoring program, the NAMS locations should not be selected a priori. Instead, the NAMS sites should be selected from Core SLAMS monitoring locations (which in turn are selected from operational SLAMS or SPM monitors), and after data collection of 1-2 years. Candidate sites would be proposed by the States and EPA Regional Office and submitted to Headquarters for approval.

5.0 ANNUAL PM SURVEILLANCE REVIEW AND REPORTING

The national air quality surveillance networks must be dynamic in order to respond to changes in pollution patterns and the needs of the air management program. On an annual basis, a report would be submitted to EPA which details proposed changes to existing networks and to summarize the performance during the previous year. This report can be viewed as the findings from the required annual network review and constitutes an annual revision to State monitoring plan.

Proposed changes to the existing networks may include modification to the number, size or boundaries of monitoring areas; number and location of PM SLAMS; number or location of Core PM-fine SLAMS sites; Core PM-fine SLAMS to be designated PM-fine NAMS and PM SLAMS to be designated PM NAMS. SLAMS with exceedances should be considered to become new or replacement Core site and SPM with exceedances could become part of the SLAMS network. The proposed changes should be developed in close consultation with the appropriate EPA Regional Office and the plan would be submitted to the appropriate Regional Office for approval. The portion of the plan that pertains to NAMS sites shall be submitted to the Administrator (through the appropriate Regional Office)

The annual report would contain certification that SLAMS data submitted to EPA is accurate and in conformance with applicable Pt. 58 requirements. There would be an additional certification that SPM data submitted to EPA is similarly accurate and in conformance with applicable Pt. 58 requirements or other requirements as approved by the RA, if this data is intended to be used for State Implementation Plan (SIP) purposes. A new brief narrative report would also be required to describe the findings of the annual SLAMS network review, reflecting within year and proposed changes to the State air quality surveillance system, to provide information on SPMs and other sites described in the plan whose data is not submitted to EPA (including number of monitoring stations, general locations, monitoring objective, scale of measurement and appropriate concentration statistics to characterize PM air quality such as number of measurements, averaging time, max, min, average concentration). The latter is needed for EPA to ensure that a proper mix of permanent, and temporary monitoring locations are utilized, that populated areas throughout the nation are monitored and to provide needed flexibility in the State monitoring program. The content of this brief report shall be in accordance with EPA guidance, to be developed.

5.1 Data Reporting

Only the total mass derived from PM-10 and PM-fine SLAMS (including Core and NAMS) monitoring sites would be required to be submitted to EPA. This is consistent with current requirements. However, EPA would encourage the reporting of all data from monitors proposed in the State monitoring plan. This would include data from SPMs and compositional data from all monitors.

6.0 NETWORK COMPLETION SCHEDULES

The new monitoring rules (i.e. Pt. 58) would become effective 6 months after promulgation of a new PM NAAQS. This will provide the States with additional time to procure new REM monitors whose specifications would be promulgated with the NAAQS. The monitoring regulations would specify schedules for the completion of the overall SLAMS networks and are described below. This includes the Core and NAMS sub-networks for which specific numbers of monitors are required. No schedules nor specific numbers of monitors would be specified for SPMs or other suggested monitoring.

6.1 SLAMS Networks

The PM-10 SLAMS networks would be expected to be completed within 6 months of Part 58 promulgation. For PM-fine, a 3-year phase-in would be utilized. During the first year, all Core PM-fine SLAMS would be required for at least one MPA per State. This area would be selected by the State according to the likelihood of violating the PM-fine NAAQS and according to the size of the affected population. More sites and planning areas would obviously be desirable and are encouraged especially in the most populated States. For the second year, all other Core population-oriented sites, including all NAMS would be required. Finally, during the third year, all Core background and transport sites and any additional required PM-fine (non-Core) SLAMS sites would be deployed. This proposed phase-in is somewhat fluid and in the final analysis will depend on costs and available resources. Tentative analyses of the requirements discussed in this paper suggest that a minimum of 100 sites will be needed for the first year, approximately 250 to 400 could be deployed the second year, and an additional 250 to 400 sites during the third year. This would correspond to a mature network of 600-900 sites. With more resources, an even larger network of 1200 sites might be reasonable.

6.2 NAMS Networks

As previously mentioned, only limited changes are planned for the PM-10 NAMS network. The PM-fine NAMS network will follow the establishment of the PM-fine Core sites. The NAMS network plan would be submitted to EPA within 12 months of the effective date of Part 58 promulgation. This plan will principally focus on the development of the new PM-fine network which would be expected to be completed within 2 years.

Table 1. Types of PM Networks 1

Network	Monitoring Objectives	Represents	Measurement Method	Sampling Frequency
M	P	S	B	T1
SLAMS
Core SLAMS	REM	every day
category "a"

pop-oriented	area of high concentration
category "b"

pop-oriented	typical community-wide exposure
background and transport	regional background

and transport
NAMS	long-term trends	REM	every day
Other SLAMS	ambient air	REM	at least

once in 6 days
SPMs	ambient air	any	any
1 Core sites and transport monitoring objective are only applicable to PM-fine

Monitoring Objectives

M =	max concentration

P =	population exposure

S =	source oriented monitoring

B =	background

T =	regional transport

Glossary of Terms

SLAMS	State and Local Air Monitoring Stations

Core SLAMS	- SLAMS which are required to sample everyday

NAMS	- SLAMS which are intended for long term trends

SPMs	Special Purpose Monitors

Category a site	Core SLAMS (or NAMS) population-oriented site located in area of expected maximum concentration

Category b site	Core site located in area of poor air quality with maximum population impact.

REM	Reference or equivalent method, i.e. Federal Reference Method or equivalent according to 40 CFR 50 and 40 CFR 53

Table 2. Size of Air Surveillance Monitoring Networks (1994)
POLLUTANT	SLAMS	NAMS	SPM*	TOTAL
PM-10	920	317	277	1514
Pb	194	109	137	440
SO2	300	195	194	689
CO	343	126	93	562
O3	516	260	144	920
NO2	200	73	84	357
*includes industrial, tribal, TVA, etc.

Table 3. Proposed PM-fine NAMS by EPA Region (Goals)
Number of

PM-fine NAMS	Frequency Distributions (percent)

EPA Region	PM-fine NAMS

(Target no. of sites =250)

Metropolitan Areas

317 PM-10

NAMS
I	15-20	6-8	7.5	7.6
II	20-30	8-12	8.4	7.3
III	20-25	8-10	9.3	8.2
IV	35-50	14-20	20.4	11.7
V	35-50	14-20	16.2	17.7
VI	25-35	10-14	13.7	11.7
VII	10-15	4-6	5.4	5.1
VIII	10-15	4-6	5.4	4.8
IX	25-40	10-16	9.6	19.0
X	10-15	4-6	4.2	6.6
TOTAL	205-295	82-118	100.0	100.0
NOTE: Among the number of NAMS per region, 1-3 "Regional Transport" sites would be required.