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

*2.5*

*2.5*are met, specifically the primary and secondary annual and 24-hour PM

*2.5*NAAQS specified in § 50.7, 50.13, and 50.18. PM

*2.5*is defined, in general terms, as particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers. PM

*2.5*mass concentrations are 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. Only those FRM, FEM, and ARM measurements that are derived in accordance with part 58 of this chapter (i.e., that are deemed “suitable”) shall be used in comparisons with the PM

*2.5*NAAQS. The data handling and computation procedures to be used to construct annual and 24-hour NAAQS metrics from reported PM

*2.5*mass concentrations, and the associated instructions for comparing these calculated metrics to the levels of the PM

*2.5*NAAQS, are specified in sections 2.0, 3.0, and 4.0 of this appendix.

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

*Air Quality System (AQS)*is EPA's official repository of ambient air data.

*Collocated monitors*refers to two or more air measurement instruments for the same parameter (e.g., PM

*2.5*mass) operated at the same site location, and whose placement is consistent with § 53.1 of this chapter. For purposes of considering a combined site record in this appendix, when two or more monitors are operated at the same site, one monitor is designated as the “primary” monitor with any additional monitors designated as “collocated.” It is implicit in these appendix procedures that the primary monitor and collocated monitor(s) are all deemed suitable for the applicable NAAQS comparison; however, it is not a requirement that the primary and monitors utilize the same specific sampling and analysis method.

*Combined site data record*is the data set used for performing calculations in appendix N. It represents data for the primary monitors augmented with data from collocated monitors according to the procedure specified in section 3.0(d) of this appendix.

*Creditable samples*are daily values in the combined site record that are given credit for data completeness. The number of creditable samples (cn) for a given year also governs which value in the sorted series of daily values represents the 98th percentile for that year. Creditable samples include daily values collected on scheduled sampling days and valid make-up samples taken for missed or invalidated samples on scheduled sampling days.

*Daily values*refer to the 24-hour average concentrations of PM

*2.5*mass measured (or averaged from hourly measurements in AQS) from midnight to midnight (local standard time) from suitable monitors.

*Data substitution tests*are diagnostic evaluations performed on an annual PM

*2.5*NAAQS design value (DV) or a 24-hour PM

*2.5*NAAQS DV to determine if those metrics, which are judged to be based on incomplete data in accordance with 4.1(b) or 4.2(b) of this appendix shall nevertheless be deemed valid for NAAQS comparisons, or alternatively, shall still be considered incomplete and not valid for NAAQS comparisons. There are two data substitution tests, the “minimum quarterly value” test and the “maximum quarterly value” test.

*Design values (DVs)*are the 3-year average NAAQS metrics that are compared to the NAAQS levels to determine when a monitoring site meets or does not meet the NAAQS, calculated as shown in section 4. There are two separate DVs specified in this appendix:

*2.5*annual mean mass concentrations for each eligible monitoring site is referred to as the “

*annual PM*

*2.5*

*NAAQS DV*”.

*2.5*mass concentration values recorded at each eligible monitoring site is referred to as the “

*24-hour (or daily) PM*

*2.5*

*NAAQS DV*”.

*Eligible sites*are monitoring stations that meet the criteria specified in § 58.11 and § 58.30 of this chapter, and thus are approved for comparison to the annual PM

*2.5*NAAQS. For the 24-hour PM

*2.5*NAAQS, all site locations that meet the criteria specified in § 58.11 are approved (i.e., eligible) for NAAQS comparisons.

*Extra samples*are non-creditable samples. They are daily values that do not occur on scheduled sampling days and that cannot be used as make-up samples for missed or invalidated scheduled samples. Extra samples are used in mean calculations and are included in the series of all daily values subject to selection as a 98th percentile value, but are not used to determine which value in the sorted list represents the 98th percentile.

*Make-up samples*are samples collected to take the place of missed or invalidated required scheduled samples. Make-up samples can be made by either the primary or the collocated monitor. Make-up samples are either taken before the next required sampling day or exactly one week after the missed (or voided) sampling day.

*maximum quarterly value data substitution test*substitutes actual “high” reported daily PM

*2.5*values from the same site (specifically, the highest reported non-excluded quarterly value(s) (year non-specific) contained in the combined site record for the evaluated 3-year period) for missing daily values.

*minimum quarterly value data substitution test*substitutes actual “low” reported daily PM

*2.5*values from the same site (specifically, the lowest reported quarterly value(s) (year non-specific) contained in the combined site record for the evaluated 3-year period) for missing daily values.

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

*2.5*mass monitoring data below which no more than 98 percent of all daily values fall using the ranking and selection method specified in section 4.5(a) of this appendix.

*Primary monitors*are suitable monitors designated by a state or local agency in their annual network plan (and in AQS) as the default data source for creating a combined site record for purposes of NAAQS comparisons. If there is only one suitable monitor at a particular site location, then it is presumed to be a primary monitor.

*Quarter*refers to a calendar quarter (e.g., January through March).

*Quarterly data capture rate*is the percentage of scheduled samples in a calendar quarter that have corresponding valid reported sample values. Quarterly data capture rates are specifically calculated as the number of creditable samples for the quarter divided by the number of scheduled samples for the quarter, the result then multiplied by 100 and rounded to the nearest integer.

*Scheduled PM*

*2.5*

*samples*refers to those reported daily values which are consistent with the required sampling frequency (per § 58.12 of this chapter) for the primary monitor, or those that meet the special exception noted in section 3.0(e) of this appendix.

*Seasonal sampling*is the practice of collecting data at a reduced frequency during a season of expected low concentrations.

*Suitable monitors*are instruments that use sampling and analysis methods approved for NAAQS comparisons. For the annual and 24-hour PM

*2.5*NAAQS, suitable monitors include all FRMs, and all FEMs/ARMs except those specific continuous FEMs/ARMs disqualified by a particular monitoring agency network in accordance with § 58.10(b)(13) and approved by the EPA Regional Administrator per § 58.11(e) of this chapter.

*Test design values (TDV)*are numerical values that used in the data substitution tests described in sections 4.1(c)(i), 4.1(c)(ii) and 4.2(c)(i) of this appendix to determine if the PM

*2.5*NAAQS DV with incomplete data are judged to be valid for NAAQS comparisons. There are two TDVs: TDV

*min*to determine if the NAAQS is not met and is used in the “minimum quarterly value” data substitution test and TDV

*max*to determine if the NAAQS is met and is used in the “maximum quarterly value” data substitution test. These TDV's are derived by substituting historically low or historically high daily concentration values for missing data in an incomplete year(s).

*Year*refers to a calendar year.

*2.5*NAAQS.

*2.5*.

*2.5*. Exceptions to the specified sampling frequencies, such as seasonal sampling, are subject to the approval of the EPA Regional Administrator and must be documented in the state or local agency Annual Monitoring Network Plan as required in § 58.10 of this chapter and also in AQS.

*2.5*

*2.5*mass concentration data produced by suitable monitors that are required to be submitted to AQS, or otherwise available to EPA, meeting the requirements of part 58 of this chapter including appendices A, C, and E shall be used in the DV calculations. Generally, EPA will only use such data if they have been certified by the reporting organization (as prescribed by § 58.15 of this chapter); however, data not certified by the reporting organization can nevertheless be used, if the deadline for certification has passed and EPA judges the data to be complete and accurate.

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

^{3}) to at least one decimal place. If concentrations are reported to one decimal place, additional digits to the right of the tenths decimal place shall be truncated. If concentrations are reported to AQS with more than one decimal place, AQS will truncate the value to one decimal place for NAAQS usage (i.e., for implementing the procedures in this appendix). In situations where suitable PM

*2.5*data are available to EPA but not reported to AQS, the same truncation protocol shall be applied to that data. In situations where PM

*2.5*mass data are submitted to AQS, or are otherwise available, with less precision than specified above, these data shall nevertheless still be deemed appropriate for NAAQS usage.

*2.5*concentration data for each corresponding day of the year and the result will be stored in the first, or start, hour (i.e., midnight, hour ‘0’) of the 24-hour period. A 24-hour average concentration shall be considered valid if at least 75 percent of the hourly averages (i.e., 18 hourly values) for the 24-hour period are available. In the event that less than all 24 hourly average concentrations are available (i.e., less than 24, but at least 18), the 24-hour average concentration shall be computed on the basis of the hours available using the number of available hours within the 24-hour period as the divisor (e.g., 19, if 19 hourly values are available). Twenty-four-hour periods with seven or more missing hours shall also be considered valid if, after substituting zero for all missing hourly concentrations, the resulting 24-hour average daily value is greater than the level of the 24-hour PM

*2.5*NAAQS (i.e., greater than or equal to 35.5 µg/m

^{3}). Twenty-four hour average PM

*2.5*mass concentrations that are averaged in AQS from hourly values will be truncated to one decimal place, consistent with the data handling procedure for the reported hourly (and also 24-hour filter-based) data.

*2.5*mass concentrations for a site shall consist of the measured concentrations recorded from the designated primary monitor(s). All daily values produced by the primary monitor are considered part of the site record; this includes all creditable samples and all extra samples.

*2.5*NAAQS

*2.5*NAAQS

*2.5*NAAQS is met when the annual PM

*2.5*NAAQS DV is less than or equal to 12.0 µg/m

^{3}at each eligible monitoring site. The secondary annual PM

*2.5*NAAQS is met when the annual PM

*2.5*NAAQS DV is less than or equal to 15.0 µg/m

^{3}at each eligible monitoring site.

*2.5*NAAQS DV. A year meets data completeness requirements when quarterly data capture rates for all four quarters are at least 75 percent. However, years with at least 11 creditable samples in each quarter shall also be considered valid if the resulting annual mean or resulting annual PM

*2.5*NAAQS DV (rounded according to the conventions of section 4.3 of this appendix) is greater than the level of the applicable primary or secondary annual PM

*2.5*NAAQS. Furthermore, where the explicit 75 percent data capture and/or 11 sample minimum requirements are not met, the 3-year annual PM

*2.5*NAAQS DV shall still be considered valid if it passes at least one of the two data substitution tests stipulated below.

*2.5*NAAQS DV, the annual PM

*2.5*NAAQS DV shall nevertheless be considered valid if one of the test conditions specified in sections 4.1(c)(i) and 4.1(c)(ii) of this appendix is met.

*2.5*NAAQS DV that is above the level of the NAAQS can be validated if it passes the minimum quarterly value data substitution test. This type of data substitution is permitted only if there are at least 30 days across the three quarters of the three years under consideration (e.g., collectively, quarter 1 of year 1, quarter 1 of year 2 and quarter 1 of year 3) from which to select the quarter-specific low value. Data substitution will be performed in all quarter periods that have less than 11 creditable samples.

*Procedure:*Identify for each deficient quarter (i.e., those with less than 11 creditable samples) the lowest reported daily value for that quarter, looking across those three months of all three years under consideration. If after substituting the lowest reported daily value for a quarter for (11− cn) daily values in the matching deficient quarter(s) (i.e., to bring the creditable number for those quarters up to 11), the procedure yields a recalculated annual PM

*2.5*NAAQS test DV (TDV

*min*) that is greater than the level of the standard, then the annual PM

*2.5*NAAQS DV is deemed to have passed the diagnostic test and is valid, and the annual PM

*2.5*NAAQS is deemed to have been violated in that 3-year period.

*2.5*NAAQS DV that is equal to or below the level of the NAAQS can be validated if it passes the maximum quarterly value data substitution test. This type of data substitution is permitted only if there is at least 50 percent data capture in each quarter that is deficient of 75 percent data capture in each of the three years under consideration. Data substitution will be performed in all quarter periods that have less than 75 percent data capture but at least 50 percent data capture. If any quarter has less than 50 percent data capture then this substitution test cannot be used.

*Procedure:*Identify for each deficient quarter (i.e., those with less than 75 percent but at least 50 percent data capture) the highest reported daily value for that quarter, excluding state-flagged data affected by exceptional events which have been approved for exclusion by the Administrator, looking across those three quarters of all three years under consideration. If after substituting the highest reported daily PM

*2.5*value for a quarter for all missing daily data in the matching deficient quarter(s) (i.e., to make those quarters 100 percent complete), the procedure yields a recalculated annual PM

*2.5*NAAQS test DV (TDV

*max*) that is less than or equal to the level of the standard, then the annual PM

*2.5*NAAQS DV is deemed to have passed the diagnostic test and is valid, and the annual PM

*2.5*NAAQS is deemed to have been met in that 3-year period.

*2.5*NAAQS DV based on data that do not meet the completeness criteria stated in 4(b) and also do not satisfy the test conditions specified in section 4(c), may also be considered valid with the approval of, or at the initiative of, the EPA Administrator, who may consider factors such as monitoring site closures/moves, monitoring diligence, the consistency and levels of the daily values that are available, and nearby concentrations in determining whether to use such data.

*2.5*NAAQS DVs are given in section 4.4 of this appendix.

*2.5*NAAQS

*2.5*NAAQS are met when the 24-hour PM

*2.5*NAAQS DV at each eligible monitoring site is less than or equal to 35 µg/m

^{3}.

*2.5*98th percentile mass concentrations are required to produce a valid 24-hour PM

*2.5*NAAQS DV. A year meets data completeness requirements when quarterly data capture rates for all four quarters are at least 75 percent. However, years shall be considered valid, notwithstanding quarters with less than complete data (even quarters with less than 11 creditable samples, but at least one creditable sample must be present for the year), if the resulting annual 98th percentile value or resulting 24-hour NAAQS DV (rounded according to the conventions of section 4.3 of this appendix) is greater than the level of the standard. Furthermore, where the explicit 75 percent quarterly data capture requirement is not met, the 24-hour PM

*2.5*NAAQS DV shall still be considered valid if it passes the maximum quarterly value data substitution test.

*2.5*NAAQS DV, the 24-hour PM

*2.5*NAAQS DV shall nevertheless be considered valid if the test conditions specified in section 4.2(c)(i) of this appendix are met.

*2.5*24-hour mass NAAQS DV that is equal to or below the level of the NAAQS can be validated if it passes the maximum quarterly value data substitution test. This type of data substitution is permitted only if there is at least 50 percent data capture in each quarter that is deficient of 75 percent data capture in each of the three years under consideration. Data substitution will be performed in all quarters that have less than 75 percent data capture but at least 50 percent data capture. If any quarter has less than 50 percent data capture then this substitution test cannot be used.

*Procedure:*Identify for each deficient quarter (i.e., those with less than 75 percent but at least 50 percent data capture) the highest reported daily PM

*2.5*value for that quarter, excluding state-flagged data affected by exceptional events which have been approved for exclusion by the Regional Administrator, looking across those three quarters of all three years under consideration. If, after substituting the highest reported daily maximum PM

*2.5*value for a quarter for all missing daily data in the matching deficient quarter(s) (i.e., to make those quarters 100 percent complete), the procedure yields a recalculated 3-year 24-hour NAAQS test DV (TDV

*max*) less than or equal to the level of the standard, then the 24-hour PM

*2.5*NAAQS DV is deemed to have passed the diagnostic test and is valid, and the 24-hour PM

*2.5*NAAQS is deemed to have been met in that 3-year period.

*2.5*NAAQS DV based on data that do not meet the completeness criteria stated in section 4(b) of this appendix and also do not satisfy the test conditions specified in section 4(c) of this appendix, may also be considered valid with the approval of, or at the initiative of, the EPA Administrator, who may consider factors such as monitoring site closures/moves, monitoring diligence, the consistency and levels of the daily values that are available, and nearby concentrations in determining whether to use such data.

*2.5*NAAQS DVs are given in section 4.5 of this appendix.

*2.5*NAAQS DVs 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*NAAQS DVs shall be rounded to the nearest tenth of a µg/m

^{3}(decimals x.x5 and greater are rounded up to the next tenth, and any decimal lower than x.x5 is rounded down to the nearest tenth).

*2.5*NAAQS DVs 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*= the mean for quarter q of the year y;

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

*i q,y*= the i

*th*value in quarter q for year y.

*y*= the annual mean concentration for year

*y*(

*y*= 1, 2, or 3); and

*q,y*= the mean for quarter

*q*of year

*y*(result of equation 1).

*2.5*NAAQS DV is calculated using equation 3 of this appendix:

*2.5*NAAQS DV; and

*y*= the annual mean for year

*y*(result of equation 2)

*2.5*NAAQS DV is rounded according to the conventions in section 4.3 of this appendix before comparisons with the levels of the primary and secondary annual PM

*2.5*NAAQS are made.

*2.5*NAAQS

*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 value 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 for the annual creditable number of samples for year y (cn

*y*) (e.g., for 120 creditable samples per year, the appropriate range would be 101 to 150). The corresponding “n” value in the right column identifies the rank of the annual 98th percentile value in the descending sorted list of site specific daily values for year y (e.g., for the range of 101 to 150, n would be 3). Thus, P

*0.98, y*= the n

*th*largest value (e.g., for the range of 101 to 150, the 98th percentile value would be the third highest value in the sorted series of daily values.

Annual number of creditable samples for year y (cny) |
The 98th percentile for year y (P0.98,y), is the nth maximum 24-hour average value for the year where n is the listed number |
---|---|

1 to 50 | 1 |

51 to 100 | 2 |

101 to 150 | 3 |

151 to 200 | 4 |

201 to 250 | 5 |

251 to 300 | 6 |

301 to 350 | 7 |

351 to 366 | 8 |

*2.5*NAAQS DV is then calculated by averaging the annual 98th percentiles using equation 4 of this appendix: P

*0.98,y*

*0.98*= the 24-hour PM

*2.5*NAAQS DV; and

*P*

*0.98, y*= the annual 98th percentile for year

*y*

*2.5*NAAQS DV is rounded according to the conventions in section 4.3 of this appendix before a comparison with the level of the primary and secondary 24-hour NAAQS are made.

**Title 40 published on 2015-07-01**.

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 2015-07-01**

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

GPO FDSys XML | Text type regulations.gov FR Doc. 2015-26594 RIN 2060-AP38 EPA-HQ-OAR-2008-0699 FRL-9933-18-OAR ENVIRONMENTAL PROTECTION AGENCY Final rule. The final rule is effective on December 28, 2015. 40 CFR Parts 50, 51, 52, 53, and 58 Based on its review of the air quality criteria for ozone (O 3 ) and related photochemical oxidants and national ambient air quality standards (NAAQS) for O 3, the Environmental Protection Agency (EPA) is revising the primary and secondary NAAQS for O 3 to provide requisite protection of public health and welfare, respectively. The EPA is revising the levels of both standards to 0.070 parts per million (ppm), and retaining their indicators (O 3 ), forms (fourth-highest daily maximum, averaged across three consecutive years) and averaging times (eight hours). The EPA is making corresponding revisions in data handling conventions for O 3 and changes to the Air Quality Index (AQI); revising regulations for the prevention of significant deterioration (PSD) program to add a transition provision for certain applications; and establishing exceptional events schedules and providing information related to implementing the revised standards. The EPA is also revising the O 3 monitoring seasons, the Federal Reference Method (FRM) for monitoring O 3 in the ambient air, Federal Equivalent Method (FEM) analyzer performance requirements, and the Photochemical Assessment Monitoring Stations (PAMS) network. Along with exceptional events schedules related to implementing the revised O 3 standards, the EPA is applying this same schedule approach to other future new or revised NAAQS and removing obsolete regulatory language for expired exceptional events deadlines. The EPA is making minor changes to the procedures and time periods for evaluating potential FRMs and equivalent methods, including making the requirements for nitrogen dioxide (NO 2 ) consistent with the requirements for O 3, and removing an obsolete requirement for the annual submission of Product Manufacturing Checklists by manufacturers of FRMs and FEMs for monitors of fine and coarse particulate matter. For a more detailed summary, see the Executive Summary below.