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Ozone Implementation

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PART 50-NATIONAL PRIMARY AND SECONDARY

AMBIENT AIR QUALITY STANDARDS

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

[Revised as of July 1, 2000]PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDSSec. 50.1 Definitions. 50.2 Scope. 50.3 Reference conditions. 50.4 National primary ambient air quality standards for sulfur oxides (sulfur dioxide). 50.5 National secondary ambient air quality standard for sulfur oxides (sulfur dioxide). 50.6 National primary and secondary ambient air quality standards for PM10. 50.7 National primary and secondary ambient air quality standards for particulate matter. 50.8 National primary ambient air quality standards for carbon monoxide. 50.9 National 1-hour primary and secondary ambient air quality standards for ozone. 50.10 National 8-hour primary and secondary ambient air quality standards for ozone. 50.11 National primary and secondary ambient air quality standards for nitrogen dioxide. 50.12 National primary and secondary ambient air quality standards for lead. 40 CFR 50 contains Appendix A-N (The following Appendix are included from 40 CFR 50. For a complete version go to http://www.access.gpo.gov/cgi-bin/cfrassemble.cgi?title=200040) Appendix H to Part 50--Interpretation of the 1-Hour Primary and Secondary National Ambient Air Quality Standards for Ozone Appendix I to Part 50--Interpretation of the 8-Hour Primary and Secondary National Ambient Air Quality Standards for Ozone Appendix K to Part 50--Interpretation of the National Ambient Air Quality Standards for Particulate Matter Appendix N to Part 50--Interpretation of the National Ambient Air Quality Standards for Particulate MatterSec. 50.1 Definitions.(a) As used in this part, all terms not defined herein shall have the meaning given them by the Act. (b) Act means the Clean Air Act, as amended (42 U.S.C. 1857-18571, as amended by Pub. L. 91-604). (c) Agency means the Environmental Protection Agency. (d) Administrator means the Administrator of the Environmental Protection Agency. (e) Ambient air means that portion of the atmosphere, external to buildings, to which the general public has access. (f) Reference method means a method of sampling and analyzing the ambient air for an air pollutant that is specified as a reference method in an appendix to this part, or a method that has been designated as a reference method in accordance with part 53 of this chapter; it does not include a method for which a reference method designation has been cancelled in accordance with Sec. 53.11 or Sec. 53.16 of this chapter. (g) Equivalent method means a method of sampling and analyzing the ambient air for an air pollutant that has been designated as an equivalent method in accordance with part 53 of this chapter; it does not include a method for which an equivalent method designation has been cancelled in accordance with Sec. 53.11 or Sec. 53.16 of this chapter. (h) Traceable means that a local standard has been compared and certified either directly or via not more than one intermediate standard, to a primary standard such as a National Bureau of Standards Standard Reference Material (NBS SRM), or a USEPA/NBS-approved Certified Reference Material (CRM). (i) Indian country is as defined in 18 U.S.C. 1151. [36 FR 22384, Nov. 25, 1971, as amended at 41 FR 11253, Mar. 17, 1976; 48 FR 2529, Jan. 20, 1983; 63 FR 7274, Feb. 12, 1998]Sec. 50.2 Scope.(a) National primary and secondary ambient air quality standards under section 109 of the Act are set forth in this part. (b) National primary ambient air quality standards define levels of air quality which the Administrator judges are necessary, with an adequate margin of safety, to protect the public health. National secondary ambient air quality standards define levels of air quality which the Administrator judges necessary to protect the public welfare from any known or anticipated adverse effects of a pollutant. Such standards are subject to revision, and additional primary and secondary standards may be promulgated as the Administrator deems necessary to protect the public health and welfare. (c) The promulgation of national primary and secondary ambient air quality standards shall not be considered in any manner to allow significant deterioration of existing air quality in any portion of any State or Indian country. (d) The proposal, promulgation, or revision of national primary and secondary ambient air quality standards shall not prohibit any State or Indian country from establishing ambient air quality standards for that State or area under a tribal CAA program or any portion thereof which are more stringent than the national standards. [36 FR 22384, Nov. 25, 1971, as amended at 63 FR 7274, Feb. 12, 1998]Sec. 50.3 Reference conditions.All measurements of air quality that are expressed as mass per unit volume (e.g., micrograms per cubic meter) other than for the particulate matter (PM10 and PM2.5) standards contained in Sec. 50.7 shall be corrected to a reference temperature of 25 deg.C and a reference pressure of 760 millimeters of mercury (1,013.2 millibars). Measurements of PM10 and PM2.5 for purposes of comparison to the standards contained in Sec. 50.7 shall be reported based on actual ambient air volume measured at the actual ambient temperature and pressure at the monitoring site during the measurement period. [62 FR 38711, July 18, 1997]Sec. 50.4 National primary ambient air quality standards for sulfur oxides (sulfur dioxide).(a) The level of the annual standard is 0.030 parts per million (ppm), not to be exceeded in a calendar year. The annual arithmetic mean shall be rounded to three decimal places (fractional parts equal to or greater than 0.0005 ppm shall be rounded up). (b) The level of the 24-hour standard is 0.14 parts per million (ppm), not to be exceeded more than once per calendar year. The 24-hour averages shall be determined from successive nonoverlapping 24-hour blocks starting at midnight each calendar day and shall be rounded to two decimal places (fractional parts equal to or greater than 0.005 ppm shall be rounded up). (c) Sulfur oxides shall be measured in the ambient air as sulfur dioxide by the reference method described in appendix A to this part or by an equivalent method designated in accordance with part 53 of this chapter. (d) To demonstrate attainment, the annual arithmetic mean and the second-highest 24-hour averages must be based upon hourly data that are at least 75 percent complete in each calendar quarter. A 24-hour block average shall be considered valid if at least 75 percent of the hourly averages for the 24-hour period are available. In the event that only 18, 19, 20, 21, 22, or 23 hourly averages are available, the 24-hour block average shall be computed as the sum of the available hourly averages using 18, 19, etc. as the divisor. If fewer than 18 hourly averages are available, but the 24-hour average would exceed the level of the standard when zeros are substituted for the missing values, subject to the rounding rule of paragraph (b) of this section, then this shall be considered a valid 24-hour average. In this case, the 24-hour block average shall be computed as the sum of the available hourly averages divided by 24. [61 FR 25579, May 22, 1996]Sec. 50.5 National secondary ambient air quality standard for sulfur oxides (sulfur dioxide).(a) The level of the 3-hour standard is 0.5 parts per million (ppm), not to be exceeded more than once per calendar year. The 3-hour averages shall be determined from successive nonoverlapping 3-hour blocks starting at midnight each calendar day and shall be rounded to 1 decimal place (fractional parts equal to or greater than 0.05 ppm shall be rounded up). (b) Sulfur oxides shall be measured in the ambient air as sulfur dioxide by the reference method described in appendix A of this part or by an equivalent method designated in accordance with part 53 of this chapter. (c) To demonstrate attainment, the second-highest 3-hour average must be based upon hourly data that are at least 75 percent complete in each calendar quarter. A 3-hour block average shall be considered valid only if all three hourly averages for the 3-hour period are available. If only one or two hourly averages are available, but the 3-hour average would exceed the level of the standard when zeros are substituted for the missing values, subject to the rounding rule of paragraph (a) of this section, then this shall be considered a valid 3-hour average. In all cases, the 3-hour block average shall be computed as the sum of the hourly averages divided by 3. [61 FR 25580, May 22, 1996]Sec. 50.6 National primary and secondary ambient air quality standards for PM10.(a) The level of the national primary and secondary 24-hour ambient air quality standards for particulate matter is 150 micrograms per cubic meter (ug/m3), 24-hour average concentration. The standards are attained when the expected number of days per calendar year with a 24-hour average concentration above 150 ug/m3, as determined in accordance with appendix K to this part, is equal to or less than one. (b) The level of the national primary and secondary annual standards for particulate matter is 50 micrograms per cubic meter ug/m3, annual arithmetic mean. The standards are attained when the expected annual arithmetic mean concentration, as determined in accordance with appendix K to this part, is less than or equal to 50 ug/m3. (c) For the purpose of determining attainment of the primary and secondary standards, particulate matter shall be measured in the ambient air as PM10 (particles with an aerodynamic diameter less than or equal to a nominal 10 micrometers) by: (1) A reference method based on appendix J and designated in accordance with part 53 of this chapter, or (2) An equivalent method designated in accordance with part 53 of this chapter. (d) The PM10 standards set forth in this section will no longer apply to an area not attaining these standards as of September 16, 1997, once EPA takes final action to promulgate a rule pursuant to section 172(e) of the Clean Air Act, as amended (42 U.S.C. 7472(e)) applicable to the area. The PM10 standards set forth in this section will no longer apply to an area attaining these standards as of September 16, 1997, once EPA approves a State Implementation Plan (SIP) applicable to the area containing all PM10 control measures adopted and implemented by the State prior to September 16, 1997, and a section 110 SIP implementing the PM standards published on July 18, 1997. SIP approvals are codified in 40 CFR part 52. [52 FR 24663, July 1, 1987, as amended at 62 FR 38711, July 18, 1997]Sec. 50.7 National primary and secondary ambient air quality standards for particulate matter.(a) The national primary and secondary ambient air quality standards for particulate matter are: (1) 15.0 micrograms per cubic meter (ug/m3) annual arithmetic mean concentration, and 65 ug/m3 24-hour average concentration measured in the ambient air as PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either: (i) A reference method based on appendix L of this part and designated in accordance with part 53 of this chapter; or (ii) An equivalent method designated in accordance with part 53 of this chapter. (2) 50 micrograms per cubic meter (ug/m3) annual arithmetic mean concentration, and 150 ug/m3 24-hour average concentration measured in the ambient air as PM10 (particles with an aerodynamic diameter less than or equal to a nominal 10 micrometers) by either: (i) A reference method based on appendix M of this part and designated in accordance with part 53 of this chapter; or (ii) An equivalent method designated in accordance with part 53 of this chapter. (b) The annual primary and secondary PM2.5 standards are met when the annual arithmetic mean concentration, as determined in accordance with Appendix N of this part, is less than or equal to 15.0 micrograms per cubic meter. (c) The 24-hour primary and secondary PM2.5 standards are met when the 98^{th}percentile 24-hour concentration, as determined in accordance with Appendix N of this part, is less than or equal to 65 micrograms per cubic meter. (d) The annual primary and secondary PM10 standards are met when the annual arithmetic mean concentration, as determined in accordance with Appendix N of this part, is less than or equal to 50 micrograms per cubic meter. (e) The 24-hour primary and secondary PM10 standards are met when the 99^{th}percentile 24-hour concentration, as determined in accordance with Appendix N of this part, is less than or equal to 150 micrograms per cubic meter. [62 FR 38711, July 18, 1997]Sec. 50.8 National primary ambient air quality standards for carbon monoxide.(a) The national primary ambient air quality standards for carbon monoxide are: (1) 9 parts per million (10 milligrams per cubic meter) for an 8- hour average concentration not to be exceeded more than once per year and (2) 35 parts per million (40 milligrams per cubic meter) for a 1- hour average concentration not to be exceeded more than once per year. (b) The levels of carbon monoxide in the ambient air shall be measured by: (1) A reference method based on appendix C and designated in accordance with part 53 of this chapter, or (2) An equivalent method designated in accordance with part 53 of this chapter. (c) An 8-hour average shall be considered valid if at least 75 percent of the hourly average for the 8-hour period are available. In the event that only six (or seven) hourly averages are available, the 8- hour average shall be computed on the basis of the hours available using six (or seven) as the divisor. (d) When summarizing data for comparision with the standards, averages shall be stated to one decimal place. Comparison of the data with the levels of the standards in parts per million shall be made in terms of integers with fractional parts of 0.5 or greater rounding up. [50 FR 37501, Sept. 13, 1985]Sec. 50.9 National 1-hour primary and secondary ambient air quality standards for ozone.(a) The level of the national 1-hour primary and secondary ambient air quality standards for ozone measured by a reference method based on appendix D to this part and designated in accordance with part 53 of this chapter, is 0.12 parts per million (235 ug/m3). The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 parts per million (235 ug/m3) is equal to or less than 1, as determined by Appendix H to this part. (b) The 1-hour standards set forth in this section will no longer apply to an area once EPA determines that the area has air quality meeting the 1-hour standard. Area designations are codified in 40 CFR part 81. [62 FR 38894, July 18, 1997]Sec. 50.10 National 8-hour primary and secondary ambient air quality standards for ozone.(a) The level of the national 8-hour primary and secondary ambient air quality standards for ozone, measured by a reference method based on appendix D to this part and designated in accordance with part 53 of this chapter, is 0.08 parts per million (ppm), daily maximum 8-hour average. (b) The 8-hour primary and secondary ozone ambient air quality standards are met at an ambient air quality monitoring site when the average of the annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.08 ppm, as determined in accordance with Appendix I to this part. [62 FR 38894, July 18, 1997]Sec. 50.11 National primary and secondary ambient air quality standards for nitrogen dioxide.(a) The level of the national primary ambient air quality standard for nitrogen dioxide is 0.053 parts per million (100 micrograms per cubic meter), annual arithmetic mean concentration. (b) The level of national secondary ambient air quality standard for nitrogen dioxide is 0.053 parts per million (100 micrograms per cubic meter), annual arithmetic mean concentration. (c) The levels of the standards shall be measured by: (1) A reference method based on appendix F and designated in accordance with part 53 of this chapter, or (2) An equivalent method designated in accordance with part 53 of this chapter. (d) The standards are attained when the annual arithmetic mean concentration in a calendar year is less than or equal to 0.053 ppm, rounded to three decimal places (fractional parts equal to or greater than 0.0005 ppm must be rounded up). To demonstrate attainment, an annual mean must be based upon hourly data that are at least 75 percent complete or upon data derived from manual methods that are at least 75 percent complete for the scheduled sampling days in each calendar quarter. [50 FR 25544, June 19, 1985]Sec. 50.12 National primary and secondary ambient air quality standards for lead.National primary and secondary ambient air quality standards for lead and its compounds, measured as elemental lead by a reference method based on appendix G to this part, or by an equivalent method, are: 1.5 micrograms per cubic meter, maximum arithmetic mean averaged over a calendar quarter. (Secs. 109, 301(a) Clean Air Act as amended (42 U.S.C. 7409, 7601(a))) [43 FR 46258, Oct. 5, 1978]

Appendix H To Part 50--Interpretation of The 1-Hour Primary and Secondary National Ambient Air Quality Standards for Ozone.1. General This appendix explains how to determine when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm (235 ug/m3) is equal to or less than 1. An expanded discussion of these procedures and associated examples are contained in the "Guideline for Interpretation of Ozone Air Quality Standards." For purposes of clarity in the following discussion, it is convenient to use the term "exceedance" to describe a daily maximum hourly average ozone measurement that is greater than the level of the standard. Therefore, the phrase "expected number of days with maximum hourly average ozone concentrations above the level of the standard" may be simply stated as the "expected number of exceedances." The basic principle in making this determination is relatively straightforward. Most of the complications that arise in determining the expected number of annual exceedances relate to accounting for incomplete sampling. In general, the average number of exceedances per calendar year must be less than or equal to 1. In its simplest form, the number of exceedances at a monitoring site would be recorded for each calendar year and then averaged over the past 3 calendar years to determine if this average is less than or equal to 1. 2. Interpretation of Expected Exceedances The ozone standard states that the expected number of exceedances per year must be less than or equal to 1. The statistical term "expected number" is basically an arithmetic average. The following example explains what it would mean for an area to be in compliance with this type of standard. Suppose a monitoring station records a valid daily maximum hourly average ozone value for every day of the year during the past 3 years. At the end of each year, the number of days with maximum hourly concentrations above 0.12 ppm is determined and this number is averaged with the results of previous years. As long as this average remains "less than or equal to 1," the area is in compliance. 3. Estimating the Number of Exceedances for a Year In general, a valid daily maximum hourly average value may not be available for each day of the year, and it will be necessary to account for these missing values when estimating the number of exceedances for a particular calendar year. The purpose of these computations is to determine if the expected number of exceedances per year is less than or equal to 1. Thus, if a site has two or more observed exceedances each year, the standard is not met and it is not necessary to use the procedures of this section to account for incomplete sampling. The term "missing value" is used here in the general sense to describe all days that do not have an associated ozone measurement. In some cases, a measurement might actually have been missed but in other cases no measurement may have been scheduled for that day. A daily maximum ozone value is defined to be the highest hourly ozone value recorded for the day. This daily maximum value is considered to be valid if 75 percent of the hours from 9:01 a.m. to 9:00 p.m. (LST) were measured or if the highest hour is greater than the level of the standard. In some areas, the seasonal pattern of ozone is so pronounced that entire months need not be sampled because it is extremely unlikely that the standard would be exceeded. Any such waiver of the ozone monitoring requirement would be handled under provisions of 40 CFR, Part 58. Some allowance should also be made for days for which valid daily maximum hourly values were not obtained but which would quite likely have been below the standard. Such an allowance introduces a complication in that it becomes necessary to define under what conditions a missing value may be assumed to have been less than the level of the standard. The following criterion may be used for ozone: A missing daily maximum ozone value may be assumed to be less than the level of the standard if the valid daily maxima on both the preceding day and the following day do not exceed 75 percent of the level of the standard. Let z denote the number of missing daily maximum values that may be assumed to be less than the standard. Then the following formula shall be used to estimate the expected number of exceedances for the year: e=v+[(v/n)*(N-n-z)] (1) (* Indicates multiplication.) where: e=the estimated number of exceedances for the year, N=the number of required monitoring days in the year, n=the number of valid daily maxima, v=the number of daily values above the level of the standard, and z=the number of days assumed to be less than the standard level. This estimated number of exceedances shall be rounded to one decimal place (fractional parts equal to 0.05 round up). It should be noted that N will be the total number of days in the year unless the appropriate Regional Administrator has granted a waiver under the provisions of 40 CFR part 58. The above equation may be interpreted intuitively in the following manner. The estimated number of exceedances is equal to the observed number of exceedances (v) plus an increment that accounts for incomplete sampling. There were (N-n) missing values for the year but a certain number of these, namely z, were assumed to be less than the standard. Therefore, (N-n-z) missing values are considered to include possible exceedances. The fraction of measured values that are above the level of the standard is v/n. It is assumed that this same fraction applies to the (N-n-z) missing values and that (v/n) x (N-n-z) of these values would also have exceeded the level of the standard. [44 FR 8220, Feb. 8, 1979, as amended at 62 FR 38895, July 18, 1997]

Appendix I to Part 50--Interpretation of the 8-Hour Primary and Secondary National Ambient Air Quality Standards for Ozone1. General. This appendix explains the data handling conventions and computations necessary for determining whether the national 8-hour primary and secondary ambient air quality standards for ozone specified in Sec. 50.10 are met at an ambient ozone air quality monitoring site. Ozone is measured in the ambient air by a reference method based on Appendix D of this part. Data reporting, data handling, and computation procedures to be used in making comparisons between reported ozone concentrations and the level of the ozone standard are specified in the following sections. Whether to exclude, retain, or make adjustments to the data affected by stratospheric ozone intrusion or other natural events is subject to the approval of the appropriate Regional Administrator. 2. Primary and Secondary Ambient Air Quality Standards for Ozone. 2.1 Data Reporting and Handling Conventions. 2.1.1 Computing 8-hour averages. Hourly average concentrations shall be reported in parts per million (ppm) to the third decimal place, with additional digits to the right being truncated. Running 8-hour averages shall be computed from the hourly ozone concentration data for each hour of the year and the result shall be stored in the first, or start, hour of the 8-hour period. An 8-hour average shall be considered valid if at least 75% of the hourly averages for the 8-hour period are available. In the event that only 6 (or 7) hourly averages are available, the 8-hour average shall be computed on the basis of the hours available using 6 (or 7) as the divisor. (8-hour periods with three or more missing hours shall not be ignored if, after substituting one-half the minimum detectable limit for the missing hourly concentrations, the 8-hour average concentration is greater than the level of the standard.) The computed 8-hour average ozone concentrations shall be reported to three decimal places (the insignificant digits to the right of the third decimal place are truncated, consistent with the data handling procedures for the reported data.) 2.1.2 Daily maximum 8-hour average concentrations. (a) There are 24 possible running 8-hour average ozone concentrations for each calendar day during the ozone monitoring season. (Ozone monitoring seasons vary by geographic location as designated in part 58, Appendix D to this chapter.) The daily maximum 8-hour concentration for a given calendar day is the highest of the 24 possible 8-hour average concentrations computed for that day. This process is repeated, yielding a daily maximum 8-hour average ozone concentration for each calendar day with ambient ozone monitoring data. Because the 8-hour averages are recorded in the start hour, the daily maximum 8-hour concentrations from two consecutive days may have some hourly concentrations in common. Generally,overlapping daily maximum 8-hour averages are not likely, except in those non-urban monitoring locations with less pronounced diurnal variation in hourly concentrations. (b) An ozone monitoring day shall be counted as a valid day if valid 8-hour averages are available for at least 75% of possible hours in the day (i.e., at least 18 of the 24 averages). In the event that less than 75% of the 8-hour averages are available, a day shall also be counted as a valid day if the daily maximum 8-hour average concentration for that day is greater than the level of the ambient standard. 2.2 Primary and Secondary Standard-related Summary Statistic. The standard-related summary statistic is the annual fourth-highest daily maximum 8-hour ozone concentration, expressed in parts per million, averaged over three years. The 3-year average shall be computed using the three most recent, consecutive calendar years of monitoring data meeting the data completeness requirements described in this appendix. The computed 3-year average of the annual fourth- highest daily maximum 8-hour average ozone concentrations shall be expressed to three decimal places (the remaining digits to the right are truncated.) 2.3 Comparisons with the Primary and Secondary Ozone Standards. (a) The primary and secondary ozone ambient air quality standards are met at an ambient air quality monitoring site when the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.08 ppm. The number of significant figures in the level of the standard dictates the rounding convention for comparing the computed 3-year average annual fourth-highest daily maximum 8-hour average ozone concentration with the level of the standard. The third decimal place of the computed value is rounded, with values equal to or greater than 5 rounding up. Thus, a computed 3-year average ozone concentration of 0.085 ppm is the smallest value that is greater than 0.08 ppm. (b) This comparison shall be based on three consecutive, complete calendar years of air quality monitoring data. This requirement is met for the three year period at a monitoring site if daily maximum 8-hour average concentrations are available for at least 90%, on average, of the days during the designated ozone monitoring season, with a minimum data completeness in any one year of at least 75% of the designated sampling days. When computing whether the minimum data completeness requirements have been met, meteorological or ambient data may be sufficient to demonstrate that meteorological conditions on missing days were not conducive to concentrations above the level of the standard. Missing days assumed less than the level of the standard are counted for the purpose of meeting the data completeness requirement, subject to the approval of the appropriate Regional Administrator. (c) Years with concentrations greater than the level of the standard shall not be ignored on the ground that they have less than complete data. Thus, in computing the 3-year average fourth maximum concentration, calendar years with less than 75% data completeness shall be included in the computation if the average annual fourth maximum 8-hour concentration is greater than the level of the standard. (d) Comparisons with the primary and secondary ozone standards are demonstrated by examples 1 and 2 in paragraphs (d)(1) and (d) (2) respectively as follows: (1) As shown in example 1, the primary and secondary standards are met at this monitoring site because the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentrations (i.e., 0.084 ppm) is less than or equal to 0.08 ppm. The data completeness requirement is also met because the average percent of days with valid ambient monitoring data is greater than 90%, and no single year has less than 75% data completeness. Example 1. Ambient monitoring site attaining the primary and secondary ozone standards Percent Highest Daily Maximum 8-hour Valid Concentration (ppm) Year Days 1st 2nd 3rd 4th 5th --------------------------------------------- 1993 100% 0.092 0.091 0.090 0.088 0.085 1994 96% 0.090 0.089 0.086 0.084 0.080 1995 98% 0.087 0.085 0.083 0.080 0.075 --------------------------------------------- Average 98% 0.084 [Examples 1 and 2 have been reformatted to fit on a 8.5" by 11" page in letter size (portrait).] (2) As shown in example 2, the primary and secondary standards are not met at this monitoring site because the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations (i.e., 0.093 ppm) is greater than 0.08 ppm. Note that the ozone concentration data for 1994 is used in these computations, even though the data capture is less than 75%, because the average fourth-highest daily maximum 8-hour average concentration is greater than 0.08 ppm. Example 2. Ambient Monitoring Site Failing to Meet the Primary and Secondary Ozone Standards Percent Highest Daily Maximum 8-hour Valid Concentration (ppm) Year Days 1st 2nd 3rd 4th 5th --------------------------------------------- 1993 96% 0.105 0.103 0.103 0.102 0.102 1994 74% 0.090 0.085 0.082 0.080 0.078 1995 98% 0.103 0.101 0.101 0.097 0.095 --------------------------------------------- Average 89% 0.093 [Examples 1 and 2 have been reformatted to fit on a 8.5" by 11" page in letter size (portrait).] 3. Design Values for Primary and Secondary Ambient Air Quality Standards for Ozone. The air quality design value at a monitoring site is defined as that concentration that when reduced to the level of the standard ensures that the site meets the standard. For a concentration-based standard, the air quality design value is simply the standard- related test statistic. Thus, for the primary and secondary ozone standards, the 3-year average annual fourth-highest daily maximum 8- hour average ozone concentration is also the air quality design value for the site. [62 FR 38895, July 18, 1997]

APPENDIX K TO PART 50-INTERPRETATION OF THE NATIONAL AMBIENT AIR QUALITY STANDARDS FOR PARTICULATE MATTER1.0 General. (a) This appendix explains the computations necessary for analyzing particulate matter data to determine attainment of the 24- hour and annual standards specified in 40 CFR 50.6. For the primary and secondary standards, particulate matter is measured in the ambient air as PM10 (particles with an aerodynamic diameter less than or equal to a nominal 10 micrometers) by a reference method based on appendix J of this part and designated in accordance with part 53 of this chapter, or by an equivalent method designated in accordance with part 53 of this chapter. The required frequency of measurements is specified in part 58 of this chapter. (b) The terms used in this appendix are defined as follows: Average refers to an arithmetic mean. All particulate matter standards are expressed in terms of expected annual values: Expected number of exceedances per year for the 24-hour standards and expected annual arithmetic mean for the annual standards. Daily value for PM10 refers to the 24-hour average concentration of PM10 calculated or measured from midnight to midnight (local time). Exceedance means a daily value that is above the level of the 24-hour standard after rounding to the nearest 10 ug/m3 (i.e., values ending in 5 or greater are to be rounded up). Expected annual value is the number approached when the annual values from an increasing number of years are averaged, in the absence of long-term trends in emissions or meteorological conditions. Year refers to a calendar year. (c) Although the discussion in this appendix focuses on monitored data, the same principles apply to modeling data, subject to EPA modeling guidelines. 2.0 Attainment Determinations. 2.1 24-Hour Primary and Secondary Standards. (a) Under 40 CFR 50.6(a) the 24-hour primary and secondary standards are attained when the expected number of exceedances per year at each monitoring site is less than or equal to one. In the simplest case, the number of expected exceedances at a site is determined by recording the number of exceedances in each calendar year and then averaging them over the past 3 calendar years. Situations in which 3 years of data are not available and possible adjustments for unusual events or trends are discussed in sections 2.3 and 2.4 of this appendix. Further, when data for a year are incomplete, it is necessary to compute an estimated number of exceedances for that year by adjusting the observed number of exceedances. This procedure, performed by calendar quarter, is described in section 3.0 of this appendix. The expected number of exceedances is then estimated by averaging the individual annual estimates for the past 3 years. (b) The comparison with the allowable expected exceedance rate of one per year is made in terms of a number rounded to the nearest tenth (fractional values equal to or greater than 0.05 are to be rounded up; e.g., an exceedance rate of 1.05 would be rounded to 1.1, which is the lowest rate for nonattainment). 2.2 Annual Primary and Secondary Standards. Under 40 CFR 50.6(b), the annual primary and secondary standards are attained when the expected annual arithmetic mean PM10 concentration is less than or equal to the level of the standard. In the simplest case, the expected annual arithmetic mean is determined by averaging the annual arithmetic mean PM10 concentrations for the past 3 calendar years. Because of the potential for incomplete data and the possible seasonality in PM10 concentrations, the annual mean shall be calculated by averaging the four quarterly means of PM10 concentrations within the calendar year. The equations for calculating the annual arithmetic mean are given in section 4.0 of this appendix. Situations in which 3 years of data are not available and possible adjustments for unusual events or trends are discussed in sections 2.3 and 2.4 of this appendix. The expected annual arithmetic mean is rounded to the nearest 1 ug/m3 before comparison with the annual standards (fractional values equal to or greater than 0.5 are to be rounded up). 2.3 Data Requirements. (a) 40 CFR 58.13 specifies the required minimum frequency of sampling for PM10. For the purposes of making comparisons with the particulate matter standards, all data produced by National Air Monitoring Stations (NAMS), State and Local Air Monitoring Stations (SLAMS) and other sites submitted to EPA in accordance with the Part 58 requirements must be used, and a minimum of 75 percent of the scheduled PM10 samples per quarter are required. (b) To demonstrate attainment of either the annual or 24-hour standards at a monitoring site, the monitor must provide sufficient data to perform the required calculations of sections 3.0 and 4.0 of this appendix. The amount of data required varies with the sampling frequency, data capture rate and the number of years of record. In all cases, 3 years of representative monitoring data that meet the 75 percent criterion of the previous paragraph should be utilized, if available, and would suffice. More than 3 years may be considered, if all additional representative years of data meeting the 75 percent criterion are utilized. Data not meeting these criteria may also suffice to show attainment; however, such exceptions will have to be approved by the appropriate Regional Administrator in accordance with EPA guidance. (c) There are less stringent data requirements for showing that a monitor has failed an attainment test and thus has recorded a violation of the particulate matter standards. Although it is generally necessary to meet the minimum 75 percent data capture requirement per quarter to use the computational equations described in sections 3.0 and 4.0 of this appendix, this criterion does not apply when less data is sufficient to unambiguously establish nonattainment. The following examples illustrate how nonattainment can be demonstrated when a site fails to meet the completeness criteria. Nonattainment of the 24-hour primary standards can be established by the observed annual number of exceedances (e.g., four observed exceedances in a single year), or by the estimated number of exceedances derived from the observed number of exceedances and the required number of scheduled samples (e.g., two observed exceedances with every other day sampling). Nonattainment of the annual standards can be demonstrated on the basis of quarterly mean concentrations developed from observed data combined with one-half the minimum detectable concentration substituted for missing values. In both cases, expected annual values must exceed the levels allowed by the standards. 2.4 Adjustment for Exceptional Events and Trends. (a) An exceptional event is an uncontrollable event caused by natural sources of particulate matter or an event that is not expected to recur at a given location. Inclusion of such a value in the computation of exceedances or averages could result in inappropriate estimates of their respective expected annual values. To reduce the effect of unusual events, more than 3 years of representative data may be used. Alternatively, other techniques, such as the use of statistical models or the use of historical data could be considered so that the event may be discounted or weighted according to the likelihood that it will recur. The use of such techniques is subject to the approval of the appropriate Regional Administrator in accordance with EPA guidance. (b) In cases where long-term trends in emissions and air quality are evident, mathematical techniques should be applied to account for the trends to ensure that the expected annual values are not inappropriately biased by unrepresentative data. In the simplest case, if 3 years of data are available under stable emission conditions, this data should be used. In the event of a trend or shift in emission patterns, either the most recent representative year(s) could be used or statistical techniques or models could be used in conjunction with previous years of data to adjust for trends. The use of less than 3 years of data, and any adjustments are subject to the approval of the appropriate Regional Administrator in accordance with EPA guidance. 3.0 Computational Equations for the 24-hour Standards. 3.1 Estimating Exceedances for a Year. (a) If PM10 sampling is scheduled less frequently than every day, or if some scheduled samples are missed, a PM10 value will not be available for each day of the year. To account for the possible effect of incomplete data, an adjustment must be made to the data collected at each monitoring location to estimate the number of exceedances in a calendar year. In this adjustment, the assumption is made that the fraction of missing values that would have exceeded the standard level is identical to the fraction of measured values above this level. This computation is to be made for all sites that are scheduled to monitor throughout the entire year and meet the minimum data requirements of section 2.3 of this appendix. Because of possible seasonal imbalance, this adjustment shall be applied on a quarterly basis. The estimate of the expected number of exceedances for the quarter is equal to the observed number of exceedances plus an increment associated with the missing data. The following equation must be used for these computations: Equation 1 >>>>40387131 See the accompanying hardcopy volume for non- machine-readable data that appears at this point. <<<< where: eq=the estimated number of exceedances for calendar quarter q; vq=the observed number of exceedances for calendar quarter q; Nq=the number of days in calendar quarter q; nq=the number of days in calendar quarter q with PM10 data; and q=the index for calendar quarter, q=1, 2, 3 or 4. (b) The estimated number of exceedances for a calendar quarter must be rounded to the nearest hundredth (fractional values equal to or greater than 0.005 must be rounded up). (c) The estimated number of exceedances for the year, e, is the sum of the estimates for each calendar quarter. Equation 2 >>>>40387132 See the accompanying hardcopy volume for non- machine-readable data that appears at this point. <<<< (d) The estimated number of exceedances for a single year must be rounded to one decimal place (fractional values equal to or greater than 0.05 are to be rounded up). The expected number of exceedances is then estimated by averaging the individual annual estimates for the most recent 3 or more representative years of data. The expected number of exceedances must be rounded to one decimal place (fractional values equal to or greater than 0.05 are to be rounded up). (e) The adjustment for incomplete data will not be necessary for monitoring or modeling data which constitutes a complete record, i.e., 365 days per year. (f) To reduce the potential for overestimating the number of expected exceedances, the correction for missing data will not be required for a calendar quarter in which the first observed exceedance has occurred if: (1) There was only one exceedance in the calendar quarter; (2) Everyday sampling is subsequently initiated and maintained for 4 calendar quarters in accordance with 40 CFR 58.13; and (3) Data capture of 75 percent is achieved during the required period of everyday sampling. In addition, if the first exceedance is observed in a calendar quarter in which the monitor is already sampling every day, no adjustment for missing data will be made to the first exceedance if a 75 percent data capture rate was achieved in the quarter in which it was observed. Example 1 a. During a particular calendar quarter, 39 out of a possible 92 samples were recorded, with one observed exceedance of the 24-hour standard. Using Equation 1, the estimated number of exceedances for the quarter is: eq=1 x 92/39=2.359 or 2.36. b. If the estimated exceedances for the other 3 calendar quarters in the year were 2.30, 0.0 and 0.0, then, using Equation 2, the estimated number of exceedances for the year is 2.362.300.00.0 which equals 4.66 or 4.7. If no exceedances were observed for the 2 previous years, then the expected number of exceedances is estimated by: (1/3) x (4.700)=1.57 or 1.6. Since 1.6 exceeds the allowable number of expected exceedances, this monitoring site would fail the attainment test. Example 2 In this example, everyday sampling was initiated following the first observed exceedance as required by 40 CFR 58.13. Accordingly, the first observed exceedance would not be adjusted for incomplete sampling. During the next three quarters, 1.2 exceedances were estimated. In this case, the estimated exceedances for the year would be 1.01.20.00.0 which equals 2.2. If, as before, no exceedances were observed for the two previous years, then the estimated exceedances for the 3-year period would then be (1/ 3) x (2.20.00.0)=0.7, and the monitoring site would not fail the attainment test. 3.2 Adjustments for Non-Scheduled Sampling Days. (a) If a systematic sampling schedule is used and sampling is performed on days in addition to the days specified by the systematic sampling schedule, e.g., during episodes of high pollution, then an adjustment must be made in the eqution for the estimation of exceedances. Such an adjustment is needed to eliminate the bias in the estimate of the quarterly and annual number of exceedances that would occur if the chance of an exceedance is different for scheduled than for non-scheduled days, as would be the case with episode sampling. (b) The required adjustment treats the systematic sampling schedule as a stratified sampling plan. If the period from one scheduled sample until the day preceding the next scheduled sample is defined as a sampling stratum, then there is one stratum for each scheduled sampling day. An average number of observed exceedances is computed for each of these sampling strata. With nonscheduled sampling days, the estimated number of exceedances is defined as: Equation 3 >>>>40387133 See the accompanying hardcopy volume for non- machine-readable data that appears at this point. <<<< where: eq=the estimated number of exceedances for the quarter; Nq=the number of days in the quarter; mq=the number of strata with samples during the quarter; vj=the number of observed exceedances in stratum j; and kj=the number of actual samples in stratum j. (c) Note that if only one sample value is recorded in each stratum, then Equation 3 reduces to Equation 1. Example 3 A monitoring site samples according to a systematic sampling schedule of one sample every 6 days, for a total of 15 scheduled samples in a quarter out of a total of 92 possible samples. During one 6-day period, potential episode levels of PM10 were suspected, so 5 additional samples were taken. One of the regular scheduled samples was missed, so a total of 19 samples in 14 sampling strata were measured. The one 6-day sampling stratum with 6 samples recorded 2 exceedances. The remainder of the quarter with one sample per stratum recorded zero exceedances. Using Equation 3, the estimated number of exceedances for the quarter is: eq=(92/14) x (2/60. . .0)=2.19. 4.0 Computational Equations for Annual Standards. 4.1 Calculation of the Annual Arithmetic Mean. (a) An annual arithmetic mean value for PM10 is determined by averaging the quarterly means for the 4 calendar quarters of the year. The following equation is to be used for calculation of the mean for a calendar quarter: Equation 4 >>>>40387141 See the accompanying hardcopy volume for non- machine-readable data that appears at this point. <<<< where: xq= the quarterly mean concentration for quarter q, q=1, 2, 3, or 4, nq= the number of samples in the quarter, and xi= the ith concentration value recorded in the quarter. (b) The quarterly mean, expressed in ug/m3, must be rounded to the nearest tenth (fractional values of 0.05 should be rounded up). (c) The annual mean is calculated by using the following equation: Equation 5 >>>>40387142 See the accompanying hardcopy volume for non- machine-readable data that appears at this point. <<<< where: x=the annual mean; and xq=the mean for calendar quarter q. (d) The average of quarterly means must be rounded to the nearest tenth (fractional values of 0.05 should be rounded up). (e) The use of quarterly averages to compute the annual average will not be necessary for monitoring or modeling data which results in a complete record, i.e., 365 days per year. (f) The expected annual mean is estimated as the average of three or more annual means. This multi-year estimate, expressed in ug/m3, shall be rounded to the nearest integer for comparison with the annual standard (fractional values of 0.5 should be rounded up). Example 4 Using Equation 4, the quarterly means are calculated for each calendar quarter. If the quarterly means are 52.4, 75.3, 82.1, and 63.2 ug/m3, then the annual mean is: x = (1/4) x (52.475.382.163.2)= 68.25 or 68.3. 4.2 Adjustments for Non-scheduled Sampling Days. (a) An adjustment in the calculation of the annual mean is needed if sampling is performed on days in addition to the days specified by the systematic sampling schedule. For the same reasons given in the discussion of estimated exceedances, under section 3.2 of this appendix, the quarterly averages would be calculated by using the following equation: Equation 6 >>>>40387143 See the accompanying hardcopy volume for non- machine-readable data that appears at this point. <<<< where: xq=the quarterly mean concentration for quarter q, q=1, 2, 3, or 4; xij=the ith concentration value recorded in stratum j; kj=the number of actual samples in stratum j; and mq=the number of strata with data in the quarter. (b) If one sample value is recorded in each stratum, Equation 6 reduces to a simple arithmetic average of the observed values as described by Equation 4. Example 5 a. During one calendar quarter, 9 observations were recorded. These samples were distributed among 7 sampling strata, with 3 observations in one stratum. The concentrations of the 3 observations in the single stratum were 202, 242, and 180 ug/m3. The remaining 6 observed concentrations were 55, 68, 73, 92, 120, and 155 ug/m3. Applying the weighting factors specified in Equation 6, the quarterly mean is: xq = (1/7) x [(1/3) x (202 242 180) 155 68 73 92 120 155] = 110.1 b. Although 24-hour measurements are rounded to the nearest 10 ug/m3 for determinations of exceedances of the 24-hour standard, note that these values are rounded to the nearest 1 ug/m3 for the calculation of means. [52 FR 24667, July 1, 1987; 52 FR 26402, July 14, 1987; 52 FR 29382, Aug. 7, 1987; 52 FR 31701, Aug. 21, 1987; 62 FR 38652, July 18, 1997]

Appendix N to Part 50--Interpretation of the National Ambient Air Quality Standards for Particulate Matter1.0 General. (a) This appendix explains the data handling conventions and computations necessary for determining when the annual and 24-hour primary and secondary national ambient air quality standards for PM specified in Sec. 50.7 of this chapter are met. Particulate matter is measured in the ambient air as PM10 and PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 10 and 2.5 micrometers, respectively) by a reference method based on Appendix M of this part for PM10 and on Appendix L of this part for PM2.5 , as applicable, and designated in accordance with part 53 of this chapter, or by an equivalent method designated in accordance with part 53 of this chapter. Data handling and computation procedures to be used in making comparisons between reported PM10 and PM2.5 concentrations and the levels of the PM standards are specified in the following sections. (b) Data resulting from uncontrollable or natural events, for example structural fires or high winds, may require special consideration. In some cases, it may be appropriate to exclude these data because they could result in inappropriate values to compare with the levels of the PM standards. In other cases, it may be more appropriate to retain the data for comparison with the level of the PM standards and then allow the EPA to formulate the appropriate regulatory response. Whether to exclude, retain, or make adjustments to the data affected by uncontrollable or natural events is subject to the approval of the appropriate Regional Administrator. (c) The terms used in this appendix are defined as follows: Average and mean refer to an arithmetic mean. Daily value for PM refers to the 24-hour average concentration of PM calculated or measured from midnight to midnight (local time) for PM10 or PM2.5 . Designated monitors are those monitoring sites designated in a State PM Monitoring Network Description for spatial averaging in areas opting for spatial averaging in accordance with part 58 of this chapter. 98^{th}percentile (used for PM2.5 ) means the daily value out of a year of monitoring data below which 98 percent of all values in the group fall. 99^{th}percentile (used for PM10 ) means the daily value out of a year of monitoring data below which 99 percent of all values in the group fall. Year refers to a calendar year. (d) Sections 2.1 and 2.5 of this appendix contain data handling instructions for the option of using a spatially averaged network of monitors for the annual standard. If spatial averaging is not considered for an area, then the spatial average is equivalent to the annual average of a single site and is treated accordingly in subsequent calculations. For example, paragraph (a)(3) of section 2.1 of this appendix could be eliminated since the spatial average would be equivalent to the annual average. 2.0 Comparisons with the PM2.5 Standards. 2.1 Annual PM2.5 Standard. (a) The annual PM2.5 standard is met when the 3-year average of the spatially averaged annual means is less than or equal to 15.0 ug/m3. The 3-year average of the spatially averaged annual means is determined by averaging quarterly means at each monitor to obtain the annual mean PM2.5 concentrations at each monitor, then averaging across all designated monitors, and finally averaging for 3 consecutive years. The steps can be summarized as follows: (1) Average 24-hour measurements to obtain quarterly means at each monitor. (2) Average quarterly means to obtain annual means at each monitor. (3) Average across designated monitoring sites to obtain an annual spatial mean for an area (this can be one site in which case the spatial mean is equal to the annual mean). (4) Average 3 years of annual spatial means to obtain a 3-year average of spatially averaged annual means. (b) In the case of spatial averaging, 3 years of spatial averages are required to demonstrate that the standard has been met. Designated sites with less than 3 years of data shall be included in spatial averages for those years that data completeness requirements are met. For the annual PM2.5 standard, a year meets data completeness requirements when at least 75 percent of the scheduled sampling days for each quarter have valid data. However, years with high concentrations and more than a minimal amount of data (at least 11 samples in each quarter) shall not be ignored just because they are comprised of quarters with less than complete data. Thus, in computing annual spatially averaged means, years containing quarters with at least 11 samples but less than 75 percent data completeness shall be included in the computation if the resulting spatially averaged annual mean concentration (rounded according to the conventions of section 2.3 of this appendix) is greater than the level of the standard. (c) Situations may arise in which there are compelling reasons to retain years containing quarters which do not meet the data completeness requirement of 75 percent or the minimum number of 11 samples. The use of less than complete data is subject to the approval of the appropriate Regional Administrator. (d) The equations for calculating the 3-year average annual mean of the PM2.5 standard are given in section 2.5 of this appendix. 2.2 24-Hour PM2.5 Standard. (a) The 24-hour PM2.5 standard is met when the 3-year average of the 98^{th}percentile values at each monitoring site is less than or equal to 65 ug/m3. This comparison shall be based on 3 consecutive, complete years of air quality data. A year meets data completeness requirements when at least 75 percent of the scheduled sampling days for each quarter have valid data. However, years with high concentrations shall not be ignored just because they are comprised of quarters with less than complete data. Thus, in computing the 3-year average 98^{th}percentile value, years containing quarters with less than 75 percent data completeness shall be included in the computation if the annual 98^{th}percentile value (rounded according to the conventions of section 2.3 of this appendix) is greater than the level of the standard. (b) Situations may arise in which there are compelling reasons to retain years containing quarters which do not meet the data completeness requirement. The use of less than complete data is subject to the approval of the appropriate Regional Administrator. (c) The equations for calculating the 3-year average of the annual 98^{th}percentile values is given in section 2.6 of this appendix. 2.3 Rounding Conventions. For the purposes of comparing calculated values to the applicable level of the standard, it is necessary to round the final results of the calculations described in sections 2.5 and 2.6 of this appendix. For the annual PM2.5 standard, the 3-year average of the spatially averaged annual means shall be rounded to the nearest 0.1 ug/m3 (decimals 0.05 and greater are rounded up to the next 0.1, and any decimal lower than 0.05 is rounded down to the nearest 0.1). For the 24-hour PM2.5 standard, the 3- year average of the annual 98^{th}percentile values shall be rounded to the nearest 1 ug/m3 (decimals 0.5 and greater are rounded up to nearest whole number, and any decimal lower than 0.5 is rounded down to the nearest whole number). 2.4 Monitoring Considerations. (a) Section 58.13 of this chapter specifies the required minimum frequency of sampling for PM2.5 . Exceptions to the specified sampling frequencies, such as a reduced frequency during a season of expected low concentrations, are subject to the approval of the appropriate Regional Administrator. Section 58.14 of 40 CFR part 58 and section 2.8 of Appendix D of 40 CFR part 58, specify which monitors are eligible for making comparisons with the PM standards. In determining a spatial mean using two or more monitoring sites operating in a given year, the annual mean for an individual site may be included in the spatial mean if and only if the mean for that site meets the criterion specified in Sec. 2.8 of Appendix D of 40 CFR part 58. In the event data from an otherwise eligible site is excluded from being averaged with data from other sites on the basis of this criterion, then the 3-year mean from that site shall be compared directly to the annual standard. (b) For the annual PM2.5 standard, when designated monitors are located at the same site and are reporting PM2.5 values for the same time periods, and when spatial averaging has been chosen, their concentrations shall be averaged before an area-wide spatial average is calculated. Such monitors will then be considered as one monitor. 2.5 Equations for the Annual PM2.5 Standard. (a) An annual mean value for PM2.5 is determined by first averaging the daily values of a calendar quarter: Equation 1 [GRAPHIC] [TIFF OMITTED] TR18JY97.000 where: xq,y,s = the mean for quarter q of year y for site s; nq = the number of monitored values in the quarter; and xi,q,y,s = the i^{th}value in quarter q for year y for site s. (b) The following equation is then to be used for calculation of the annual mean: Equation 2 [GRAPHIC] [TIFF OMITTED] TR18JY97.001 where: xy,s = the annual mean concentration for year y (y = 1, 2, or 3) and for site s; and xq,y,s = the mean for quarter q of year y for site s. (c) (1) The spatially averaged annual mean for year y is computed by first calculating the annual mean for each site designated to be included in a spatial average, xy,s , and then computing the average of these values across sites: Equation 3 [GRAPHIC] [TIFF OMITTED] TR18JY97.002 where: xy = the spatially averaged mean for year y; xy,s = the annual mean for year y and site s; and ns = the number of sites designated to be averaged. (2) In the event that an area designated for spatial averaging has two or more sites at the same location producing data for the same time periods, the sites are averaged together before using Equation 3 by: Equation 4 [GRAPHIC] [TIFF OMITTED] TR18JY97.003 where: xy,s* = the annual mean for year y for the sites at the same location (which will now be considered one site); nc = the number of sites at the same location designated to be included in the spatial average; and xy,s = the annual mean for year y and site s. (d) The 3-year average of the spatially averaged annual means is calculated by using the following equation: Equation 5 [GRAPHIC] [TIFF OMITTED] TR18JY97.004 where: x = the 3-year average of the spatially averaged annual means; and xy = the spatially averaged annual mean for year y. Example 1--Area Designated for Spatial Averaging That Meets the Primary Annual PM2.5 Standard. a. In an area designated for spatial averaging, four designated monitors recorded data in at least 1 year of a particular 3-year period. Using Equations 1 and 2, the annual means for PM2.5 at each site are calculated for each year. The following table can be created from the results. Data completeness percentages for the quarter with the fewest number of samples are also shown. Table 1.--Results from Equations 1 and 2 -------------------------------------------------------------------------------------------------------------------------------------------------------- Site #1 Site #2 Site #3 Site #4 Spatial mean -------------------------------------------------------------------------------------------------------------------------------------------------------- Year 1......................................... Annual mean (ug/m\3\)............ 12.7 ............ ............ ............ 12.7 % data completeness.............. 80 0 0 0 ............ Year 2......................................... Annual mean (ug/m\3\)............ 12.6 17.5 15.2 ............ 15.05 % data completeness.............. 90 63 38 0 ............ Year 3......................................... Annual mean (ug/m\3\).... 12.5 18.5 14.1 16.9 15.50 % data completeness.............. 90 80 85 50 ............ 3-year mean.................................... ................................. ............ ............ ............ ............ 14.42 -------------------------------------------------------------------------------------------------------------------------------------------------------- b. The data from these sites are averaged in the order described in section 2.1 of this appendix. Note that the annual mean from site #3 in year 2 and the annual mean from site #4 in year 3 do not meet the 75 percent data completeness criteria. Assuming the 38 percent data completeness represents a quarter with fewer than 11 samples, site #3 in year 2 does not meet the minimum data completeness requirement of 11 samples in each quarter. The site is therefore excluded from the calculation of the spatial mean for year 2. However, since the spatial mean for year 3 is above the level of the standard and the minimum data requirement of 11 samples in each quarter has been met, the annual mean from site #4 in year 3 is included in the calculation of the spatial mean for year 3 and in the calculation of the 3-year average. The 3-year average is rounded to 14.4 ug/m3, indicating that this area meets the annual PM2.5 standard. Example 2--Area With Two Monitors at the Same Location That Meets the Primary Annual PM2.5 Standard. a. In an area designated for spatial averaging, six designated monitors, with two monitors at the same location (#5 and #6), recorded data in a particular 3-year period. Using Equations 1 and 2, the annual means for PM2.5 are calculated for each year. The following table can be created from the results. Table 2.--Results From Equations 1 and 2 -------------------------------------------------------------------------------------------------------------------------------------------------------- Average of Spatial Annual mean (ug/m\3\) Site #1 Site #2 Site #3 Site #4 Site #5 Site #6 #5 and #6 mean -------------------------------------------------------------------------------------------------------------------------------------------------------- Year 1............................................ 12.9 9.9 12.6 11.1 14.5 14.6 14.55 12.21 Year 2............................................ 14.5 13.3 12.2 10.9 16.1 16.0 16.05 13.39 Year 3............................................ 14.4 12.4 11.5 9.7 12.3 12.1 12.20 12.04 3-Year mean....................................... ........... ........... ........... ........... ........... ........... .......... 12.55 -------------------------------------------------------------------------------------------------------------------------------------------------------- b. The annual means for sites #5 and #6 are averaged together using Equation 4 before the spatial average is calculated using Equation 3 since they are in the same location. The 3-year mean is rounded to 12.6 ug/m3, indicating that this area meets the annual PM2.5 standard. Example 3--Area With a Single Monitor That Meets the Primary Annual PM2.5 Standard. a. Given data from a single monitor in an area, the calculations are as follows. Using Equations 1 and 2, the annual means for PM2.5 are calculated for each year. If the annual means are 10.28, 17.38, and 12.25 ug/m3, then the 3- year mean is: [GRAPHIC] [TIFF OMITTED] TR18JY97.005 b. This value is rounded to 13.3, indicating that this area meets the annual PM2.5 standard. 2.6 Equations for the 24-Hour PM2.5 Standard. (a) When the data for a particular site and year meet the data completeness requirements in section 2.2 of this appendix, calculation of the 98^{th}percentile is accomplished by the following steps. All the daily values from a particular site and year comprise a series of values (x1 , x2 , x3 , ..., xn ), that can be sorted into a series where each number is equal to or larger than the preceding number (x[1] , x[2] , x[3] , ..., x[n] ). In this case, x[1] is the smallest number and x[n] is the largest value. The 98^{th}percentile is found from the sorted series of daily values which is ordered from the lowest to the highest number. Compute (0.98) x (n) as the number "i.d", where "i" is the integer part of the result and "d" is the decimal part of the result. The 98^{th}percentile value for year y, P0.98, y , is given by Equation 6: Equation 6 [GRAPHIC] [TIFF OMITTED] TR18JY97.006 where: P0.98,y = 98^{th}percentile for year y; x[i+1] = the (i+1)^{th}number in the ordered series of numbers; and i = the integer part of the product of 0.98 and n. (b) The 3-year average 98^{th}percentile is then calculated by averaging the annual 98^{th}percentiles: Equation 7 [GRAPHIC] [TIFF OMITTED] TR18JY97.007 (c) The 3-year average 98^{th}percentile is rounded according to the conventions in section 2.3 of this appendix before a comparison with the standard is made. Example 4--Ambient Monitoring Site With Every-Day Sampling That Meets the Primary 24-Hour PM2.5 Standard. a. In each year of a particular 3 year period, varying numbers of daily PM2.5 values (e.g., 281, 304, and 296) out of a possible 365 values were recorded at a particular site with the following ranked values (in ug/m3): Table 3.--Ordered Monitoring Data For 3 Years ---------------------------------------------------------------------------------------------------------------- Year 1 Year 2 Year 3 ---------------------------------------------------------------------------------------------------------------- j rank Xj value j rank X j value j rank X j value ---------------------------------------------------------------------------------------------------------------- 275.............. 57.9 296 54.3 290 66.0 276.............. 59.0 297 57.1 291 68.4 277.............. 62.2 298 63.0 292 69.8 ---------------------------------------------------------------------------------------------------------------- b. Using Equation 6, the 98 ^{th}percentile values for each year are calculated as follows: [GRAPHIC] [TIFF OMITTED] TR18JY97.008 [GRAPHIC] [TIFF OMITTED] TR18JY97.009 [GRAPHIC] [TIFF OMITTED] TR18JY97.010 c. 1. Using Equation 7, the 3-year average 98^{th}percentile is calculated as follows: [GRAPHIC] [TIFF OMITTED] TR18JY97.011 2. Therefore, this site meets the 24-hour PM2.5 standard. 3.0 Comparisons with the PM10 Standards. 3.1 Annual PM10 Standard. (a) The annual PM10 standard is met when the 3-year average of the annual mean PM10 concentrations at each monitoring site is less than or equal to 50 ug/ m^{3}. The 3-year average of the annual means is determined by averaging quarterly means to obtain annual mean PM10 concentrations for 3 consecutive, complete years at each monitoring site. The steps can be summarized as follows: (1) Average 24-hour measurements to obtain a quarterly mean. (2) Average quarterly means to obtain an annual mean. (3) Average annual means to obtain a 3-year mean. (b) For the annual PM10 standard, a year meets data completeness requirements when at least 75 percent of the scheduled sampling days for each quarter have valid data. However, years with high concentrations and more than a minimal amount of data (at least 11 samples in each quarter) shall not be ignored just because they are comprised of quarters with less than complete data. Thus, in computing the 3-year average annual mean concentration, years containing quarters with at least 11 samples but less than 75 percent data completeness shall be included in the computation if the annual mean concentration (rounded according to the conventions of section 2.3 of this appendix) is greater than the level of the standard. (c) Situations may arise in which there are compelling reasons to retain years containing quarters which do not meet the data completeness requirement of 75 percent or the minimum number of 11 samples. The use of less than complete data is subject to the approval of the appropriate Regional Administrator. (d) The equations for calculating the 3-year average annual mean of the PM10 standard are given in section 3.5 of this appendix. 3.2 24-Hour PM10 Standard. (a) The 24-hour PM10 standard is met when the 3-year average of the annual 99^{th}percentile values at each monitoring site is less than or equal to 150 ug/ m^{3}. This comparison shall be based on 3 consecutive, complete years of air quality data. A year meets data completeness requirements when at least 75 percent of the scheduled sampling days for each quarter have valid data. However, years with high concentrations shall not be ignored just because they are comprised of quarters with less than complete data. Thus, in computing the 3- year average of the annual 99^{th}percentile values, years containing quarters with less than 75 percent data completeness shall be included in the computation if the annual 99^{th}percentile value (rounded according to the conventions of section 2.3 of this appendix) is greater than the level of the standard. (b) Situations may arise in which there are compelling reasons to retain years containing quarters which do not meet the data completeness requirement. The use of less than complete data is subject to the approval of the appropriate Regional Administrator. (c) The equation for calculating the 3-year average of the annual 99^{th}percentile values is given in section 2.6 of this appendix. 3.3 Rounding Conventions. For the annual PM10 standard, the 3-year average of the annual PM10 means shall be rounded to the nearest 1 ug/m3 (decimals 0.5 and greater are rounded up to the next whole number, and any decimal less than 0.5 is rounded down to the nearest whole number). For the 24-hour PM10 standard, the 3-year average of the annual 99^{th}percentile values of PM10 shall be rounded to the nearest 10 ug/m3 (155 ug/ m^{3}and greater would be rounded to 160 ug/ m^{3}and 154 ug/m3 and less would be rounded to 150 ug/m3). 3.4 Monitoring Considerations. Section 58.13 of this chapter specifies the required minimum frequency of sampling for PM10 . Exceptions to the specified sampling frequencies, such as a reduced frequency during a season of expected low concentrations, are subject to the approval of the appropriate Regional Administrator. For making comparisons with the PM10 NAAQS, all sites meeting applicable requirements in part 58 of this chapter would be used. 3.5 Equations for the Annual PM10 Standard. (a) An annual arithmetic mean value for PM10 is determined by first averaging the 24-hour values of a calendar quarter using the following equation: Equation 8 [GRAPHIC] [TIFF OMITTED] TR18JY97.012 where: xq,y = the mean for quarter q of year y; nq = the number of monitored values in the quarter; and xi,q,y = the i^{th}value in quarter q for year y. (b) The following equation is then to be used for calculation of the annual mean: Equation 9 [GRAPHIC] [TIFF OMITTED] TR18JY97.013 where: xy = the annual mean concentration for year y, (y=1, 2, or 3); and xq,y = the mean for a quarter q of year y. (c) The 3-year average of the annual means is calculated by using the following equation: Equation 10 [GRAPHIC] [TIFF OMITTED] TR18JY97.014 where: x = the 3-year average of the annual means; and xy = the annual mean for calendar year y. Example 5--Ambient Monitoring Site That Does Not Meet the Annual PM10 Standard. a. Given data from a PM10 monitor and using Equations 8 and 9, the annual means for PM10 are calculated for each year. If the annual means are 52.42, 82.17, and 63.23 ug/m3, then the 3-year average annual mean is: [GRAPHIC] [TIFF OMITTED] TR18JY97.015 b. Therefore, this site does not meet the annual PM10 standard. 3.6 Equation for the 24-Hour PM10 Standard. (a) When the data for a particular site and year meet the data completeness requirements in section 3.2 of this appendix, calculation of the 99^{th}percentile is accomplished by the following steps. All the daily values from a particular site and year comprise a series of values (x1 , x2 , x3 , ..., xn ) that can be sorted into a series where each number is equal to or larger than the preceding number (x[1] , x[2] , x[3] , ..., x[n] ). In this case, x[1] is the smallest number and x[n] is the largest value. The 99^{th}percentile is found from the sorted series of daily values which is ordered from the lowest to the highest number. Compute (0.99) x (n) as the number "i.d", where "i" is the integer part of the result and "d" is the decimal part of the result. The 99^{th}percentile value for year y, P0.99,y , is given by Equation 11: Equation 11 [GRAPHIC] [TIFF OMITTED] TR18JY97.016 where: P0.99,y = the 99^{th}percentile for year y; x[i+1] = the (i+1)^{th}number in the ordered series of numbers; and i = the integer part of the product of 0.99 and n. (b) The 3-year average 99^{th}percentile value is then calculated by averaging the annual 99^{th}percentiles: Equation 12 [GRAPHIC] [TIFF OMITTED] TR18JY97.017 (c) The 3-year average 99^{th}percentile is rounded according to the conventions in section 3.3 of this appendix before a comparison with the standard is made. Example 6--Ambient Monitoring Site With Sampling Every Sixth Day That Meets the Primary 24-Hour PM10 Standard. a. In each year of a particular 3 year period, varying numbers of PM10 daily values (e.g., 110, 98, and 100) out of a possible 121 daily values were recorded at a particular site with the following ranked values (in ug/m3): Table 4.--Ordered Monitoring Data For 3 Years ---------------------------------------------------------------------------------------------------------------- Year 1 Year 2 Year 3 ---------------------------------------------------------------------------------------------------------------- j rank Xj value j rank X j value j rank X j value ---------------------------------------------------------------------------------------------------------------- 108.............. 120 96 143 98 140 109.............. 128 97 148 99 144 110.............. 130 98 150 100 147 ---------------------------------------------------------------------------------------------------------------- b. Using Equation 11, the 99 ^{th}percentile values for each year are calculated as follows: [GRAPHIC] [TIFF OMITTED] TR18JY97.018 [GRAPHIC] [TIFF OMITTED] TR18JY97.019 [GRAPHIC] [TIFF OMITTED] TR18JY97.020 c. 1. Using Equation 12, the 3-year average 99^{th}percentile is calculated as follows: [GRAPHIC] [TIFF OMITTED] TR18JY97.021 2. Therefore, this site meets the 24-hour PM10 standard. [62 FR 38755, July 18, 1997]