# 40 CFR Part 50, Appendix N to Part 50 - Interpretation of the National Ambient Air Quality Standards for PM2.5

*2.5*

*2.5*specified in § 50.7 and § 50.13 of this part are met. PM

*2.5*, defined as particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers, is measured in the ambient air by a Federal reference method (FRM) based on appendix L of this part, as applicable, and designated in accordance with part 53 of this chapter, or by a Federal equivalent method (FEM) designated in accordance with part 53 of this chapter, or by an Approved Regional Method (ARM) designated in accordance with part 58 of this chapter. Data handling and computation procedures to be used in making comparisons between reported PM

*2.5*concentrations and the levels of the PM

*2.5*NAAQS are specified in the following sections.

*2.5*NAAQS. In other cases, it may be more appropriate to retain the data for comparison with the levels of the PM

*2.5*NAAQS and then for EPA to formulate the appropriate regulatory response.

*Annual mean*refers to a weighted arithmetic mean, based on quarterly means, as defined in section 4.4 of this appendix.

*Creditable samples*are samples that are given credit for data completeness. They include valid samples collected on required sampling days and valid “make-up” samples taken for missed or invalidated samples on required sampling days.

*Daily values*for PM

*2.5*refers to the 24-hour average concentrations of PM

*2.5*calculated (averaged from hourly measurements) or measured from midnight to midnight (local standard time) that are used in NAAQS computations.

*Designated monitors*are those monitoring sites designated in a State or local agency PM Monitoring Network Description in accordance with part 58 of this chapter.

*Design values*are the metrics (

*i.e.*, statistics) that are compared to the NAAQS levels to determine compliance, calculated as shown in section 4 of this appendix:

*annual standard design value*”). If spatial averaging has been approved by EPA for a group of sites which meet the criteria specified in section 2(b) of this appendix and section 4.7.5 of appendix D of 40 CFR part 58, then 3 years of spatially averaged annual means will be averaged to derive the

*annual standard design value*for that group of sites (further referred to as the “

*spatially averaged annual standard design value*”). Otherwise, the annual standard design value will represent the 3-year average of annual means for a single site (further referred to as the “

*single site annual standard design value*”).

*24-hour standard design value*”).

*Extra samples*are non-creditable samples. They are daily values that do not occur on scheduled sampling days and that can not be used as make-ups for missed or invalidated scheduled samples. Extra samples are used in mean calculations and are subject to selection as a 98th percentile.

*Make-up samples*are samples taken to supplant missed or invalidated required scheduled samples. Make-ups can be made by either the primary or the collocated instruments. Make-up samples are either taken before the next required sampling day or exactly one week after the missed (or voided) sampling day. Also, to be considered a valid make-up, the sampling must be administered according to EPA guidance.

*98th percentile*is the daily value out of a year of PM

*2.5*monitoring data below which 98 percent of all daily values fall.

*Year*refers to a calendar year.

*2.5*standards.

*2.5*. For example, this could be demonstrated by site-specific chemical speciation profiles confirming all major component concentration averages to be within 10 percent for each calendar quarter.

*2.5*. Exceptions to the specified sampling frequencies, such as a reduced frequency during a season of expected low concentrations (

*i.e.*, “seasonal sampling”), are subject to the approval of EPA. Annual 98th percentile values are to be calculated according to equation 5 in section 4.5 of this appendix when a site operates on a “seasonal sampling” schedule.

*2.5*NAAQS and Data Reporting Considerations.

*2.5*data required to be submitted to EPA's Air Quality System (AQS) shall be used in the design value calculations.

*2.5*measurement data (typically hourly for continuous instruments and daily for filter-based instruments) shall be reported to AQS in micrograms per cubic meter (µg/m

^{3}) to one decimal place, with additional digits to the right being truncated.

*2.5*concentration data for each corresponding day of the year and the result shall be stored in the first, or start, hour (

*i.e.*, midnight, hour ‘0’) of the 24-hour period. A 24-hour average shall be considered valid if at least 75 percent (

*i.e.*, 18) of the hourly averages for the 24-hour period are available. In the event that less than all 24 hourly averages are available (

*i.e.*, less than 24, but at least 18), the 24-hour average shall be computed on the basis of the hours available using the number of available hours as the divisor (e.g., 19). 24-hour periods with seven or more missing hours shall be considered valid if, after substituting zero for all missing hourly concentrations, the 24-hour average concentration is greater than the level of the standard. The computed 24-hour average PM

*2.5*concentrations shall be reported to one decimal place (the additional digits to the right of the first decimal place are truncated, consistent with the data handling procedures for the reported data).

*i.e.*, that site's daily value); this includes all creditable samples and all extra samples.

*i.e.*, that site's daily value). If more than one valid collocated FRM/FEM/ARM value is available, the average of those valid collocated values shall be used as the daily value.

*2.5*NAAQS.

*2.5*NAAQS.

*2.5*NAAQS is met when the annual standard design value is less than or equal to 15.0 micrograms per cubic meter (µg/m

^{3}).

*2.5*NAAQS.

*2.5*NAAQS is met when the 24-hour standard design value at each monitoring site is less than or equal to 35 µg/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 shall be considered valid, notwithstanding quarters with less than complete data (even quarters with less than 11 samples), if the resulting annual 98th percentile value or resulting 24-hour standard design value (rounded according to the conventions of section 4.3 of this appendix) is greater than the level of the standard.

*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 4.4 and 4.5 of this appendix. Results for all intermediate calculations shall not be rounded.

*2.5*standard design values shall be rounded to the nearest 0.1 µg/m

^{3}(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).

*2.5*standard design values shall be rounded to the nearest 1 µg/m

^{3}(decimals 0.5 and greater are rounded up to the nearest whole number, and any decimal lower than 0.5 is rounded down to the nearest whole number).

*2.5*NAAQS.

*2.5*is determined by first averaging the daily values of a calendar quarter using equation 1 of this appendix:

*q,y,s*= the mean for quarter q of the year y for site s;

*q*= the number of daily values in the quarter; and

*i q,y,s*= the i

^{th}value in quarter q for year y for site s.

*y,s*= the annual mean concentration for year y (y = 1, 2, or 3) and for site s; and

*q,y,s*= the mean for quarter q of year y for site s.

*i.e.*, for single site comparisons), skip to equation 4.B of this appendix.

*y*= the spatially averaged mean for year y,

*y,s*= the annual mean for year y and site s for sites designated to be averaged that meet completeness criteria , and

*s*= the number of sites designated to be averaged that meet completeness criteria.

*y*= the spatially averaged annual mean for year y (result of equation 3 of this appendix) when spatial averaging is used, or

*y,s*the annual mean for year y and site s (result of equation 2 of this appendix) when spatial averaging is not used.

*2.5*NAAQS

*Regular procedure for identifying annual 98th percentile values.*Identification of annual 98th percentile values using the regular procedure (table 1) will be based on the creditable number of samples (as described below), rather than on the actual number of samples. Credit will not be granted for extra (non-creditable) samples. Extra samples, however, are candidates for selection as the annual 98th percentile. [The creditable number of samples will determine how deep to go into the data distribution, but all samples (creditable and extra) will be considered when making the percentile assignment.] The annual creditable number of samples is the sum of the four quarterly creditable number of samples.

*Procedure:*Sort all the daily values from a particular site and year by descending value. (For example: (x[1], x[2], x[3], * * *, x[n]). In this case, x[1] is the largest number and x[n] is the smallest value.) The 98th percentile is determined from this sorted series of daily values which is ordered from the highest to the lowest number. Using the left column of table 1, determine the appropriate range (

*i.e.*, row) for the annual creditable number of samples for year y (cn

*y*). The corresponding “n” value in the right column identifies the rank of the annual 98th percentile value in the descending sorted list of daily site values for year y. Thus, P

*0.98, y*= the nth largest value.

Annual creditable number of samples for year “y” (cny) |
P0.98, y is the nth maximum value of the year, where n is the listed number |
---|---|

1-50 | 1 |

51-100 | 2 |

101-150 | 3 |

151-200 | 4 |

201-250 | 5 |

251-300 | 6 |

301-350 | 7 |

351-366 | 8 |

*Procedure:*Calculate the annual 98th percentiles by determining the smallest measured concentration, x, that makes W(x) greater than 0.98 using equation 5 of this appendix:

*High*= number of calendar days in the “High” season;

*Low*= number of calendar days in the “Low” season;

*High*d

*Low*= days in a year; and

*High*/(d

*High*d

*Low*) and d

*Low*/(d

*High*d

*Low*)” are constant and are called seasonal “weights.”

**Title 40 published on 2013-07-01**

The following are only the Rules published in the Federal Register **after** the published date of Title 40.

For a complete list of all Rules, Proposed Rules, and Notices view the Rulemaking tab.

**Title 40 published on 2013-07-01**

The following are **ALL** rules, proposed rules, and notices (chronologically) published in the Federal Register relating to *40 CFR 50* **after** this date.

GPO FDSys XML | Text type regulations.gov FR Doc. 2014-03116 RIN FRL-9906-45-ORD Docket No. ID No. EPA-HQ-OAR-2014-0128 ENVIRONMENTAL PROTECTION AGENCY Notice of workshop. The workshop will be held March 4-6, 2014. The pre-registration deadline is February 28, 2014. 40 CFR Part 50 EPA is announcing a “ Workshop to Discuss Policy-Relevant Science to Inform EPA's Review of the Secondary National Ambient Air Quality Standards (NAAQS) for Oxides of Nitrogen and Sulfur .” This workshop is being organized by EPA's Office of Research and Development's, National Center for Environmental Assessment (NCEA) and the Office of Air and Radiation's, Office of Air Quality Planning and Standards (OAQPS). The workshop will be held March 4-6, 2014, in Research Triangle Park, North Carolina, and it will be open to attendance by interested public observers on a first-come, first-served basis up to the limits of available space.

GPO FDSys XML | Text type regulations.gov FR Doc. C1-2013-13233 RIN 2060-AR34 EPA-HQ-OAR-2010-0885, FRL-9810-3 ENVIRONMENTAL PROTECTION AGENCY 40 CFR Parts 50, 51, 70 and 71

GPO FDSys XML | Text type regulations.gov FR Doc. 2013-17830 RIN EPA-HQ-OAR-2010-0885, FRL-9836-5 ENVIRONMENTAL PROTECTION AGENCY Notice of extension of comment period. Comments. Comments must be received on or before September 4, 2013. 40 CFR Parts 50, 51, 70 and 71 The EPA is announcing an extension of the public comment period on the Proposed Rule Regarding “Implementation of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation Plan Requirements” (June 6, 2013). The EPA is extending the comment period that originally was scheduled to end on August 5, 2013. The extended comment period will close on September 4, 2013. The EPA is extending the comment period because of a request we received in a timely manner.

GPO FDSys XML | Text type regulations.gov FR Doc. 2013-15880 RIN 2060-AP89 EPA-HQ-OAR-2012-0210 FRL-9822-1 ENVIRONMENTAL PROTECTION AGENCY Final rule. This final rule is effective on August 2, 2013. 40 CFR Part 50 The EPA is establishing a new Federal Reference Method (FRM) for measuring Lead (Pb) in total suspended particulate matter (TSP) collected from ambient air. This method is intended for use by analytical laboratories performing the analysis of Pb in TSP to support data collection for the Pb National Ambient Air Quality Standard (NAAQS). The existing FRM for Pb is designated as a new Federal Equivalent Method (FEM), and the currently designated FEMs are retained. This action avoids any disruption to existing Pb monitoring networks and data collection and does not affect the FRM for TSP sample collection (High-Volume Method).