Reviewing National Ambient Air Quality Standards – Scientific and Technical Information

#
Particulate Matter (PM) Standards -

Table of Historical PM NAAQS

**History of the National Ambient Air Quality Standards for Particulate Matter **

**During the Period 1971-2012**

Final Rule |
Primary/ Secondary | Indicator |
Averaging Time |
Level ^{(1)} |
Form |
---|---|---|---|---|---|

1971
36 FR 8186 Apr 30, 1971 |
Primary | TSP ^{(2)} |
24-hour | 260 µg/m^{3} |
Not to be exceeded more than once per year |

Annual | 75 µg/m^{3} |
Annual geometric mean | |||

Secondary | TSP | 24-hour | 150 µg/m^{3} |
Not to be exceeded more than once per year | |

Annual | 60 µg/m^{3} |
Annual geometric mean | |||

1987
52 FR 24634 Jul 1, 1987 |
Primary and Secondary | PM_{10} |
24-hour | 150 µg/m^{3} |
Not to be exceeded more than once per year on average over a 3-year period |

Annual | 50 µg/m^{3} |
Annual arithmetic mean, averaged over 3 years | |||

1997
62 FR 38652 Jul 18, 1997 |
Primary and Secondary | PM_{2.5} |
24-hour | 65 µg/m^{3} |
98th percentile, averaged over 3 years |

Annual | 15.0 µg/m^{3} |
Annual arithmetic mean, averaged over 3 years ^{(3),(4)} |
|||

PM_{10} |
24-hour | 150 µg/m^{3} |
Initially promulgated 99th percentile,
averaged over 3 years;
when 1997 standards for PM10 were vacated,
the form of 1987 standards remained in place
(not to be exceeded more than once per year
on average over a 3-year period) ^{(5)} |
||

Annual | 50 µg/m^{3} |
Annual arithmetic mean, averaged over 3 years | |||

2006
71 FR 61144 Oct 17, 2006 |
Primary and Secondary | PM_{2.5} |
24-hour | 35 µg/m^{3} |
98th percentile, averaged over 3 years ^{(6)} |

Annual | 15.0 µg/m^{3} |
Annual arithmetic mean, averaged over 3 years ^{(2), (7)} |
|||

PM_{10} |
24-hour ^{(8)} |
150 µg/m^{3} |
Not to be exceeded more than once per year on average over a 3-year period | ||

2012 |
Primary | PM_{2.5} |
Annual | 12.0 µg/m^{3} |
Annual arithmetic mean, averaged over 3 years ^{(2), (7)} |

Secondary | Annual | 15.0 µg/m^{3} |
Annual arithmetic mean, averaged over 3 years ^{(2), (7)} |
||

Primary and Secondary | 24-hour | 35 µg/m^{3} |
98th percentile, averaged over 3 years ^{(6)} |
||

Primary and Secondary | PM_{10} |
24-hour ^{(8)} |
150 µg/m^{3} |
Not to be exceeded more than once per year on average over a 3-year period |

^{(1)} Units of measure are micrograms per cubic meter of air (µg/m^{3}).

^{(2)} TSP = total suspended particles.

^{(3)}The level of the annual standard is defined to one decimal place (i.e., 15.0 µg/m^{3}) as determined by rounding. For example, a 3-year average annual mean of 15.04 µg/m^{3} would round to 15.0 µg/m^{3} and, thus, meet the annual standard and a 3-year average of 15.05 µg/m^{3} would round to 15.1 µg/m^{3} and, hence, violate the annual standard (40 CFR part 50 Appendix N).

^{(4)}The level of the standard was to be compared to measurements made at sites that represent “community-wide air quality” recording the highest level, or, if specific requirements were satisfied, to average measurements from multiple community-wide air quality monitoring sites (“spatial averaging”).

^{(5)} See 69 FR 45592, July 30, 2004.

^{(6)} The level of the 24-hour standard is defined as an integer (zero decimal places) as determined by rounding. For example, a 3-year average 98th percentile concentration of 35.49 µg/m^{3} would round to 35 µg/m^{3} and thus meet the 24-hour standard and a 3-year average of 35.50 µg/m^{3} would round to 36 and, hence, violate the 24-hour standard (40 CFR part 50 Appendix N).

^{(7)} The EPA tightened the constraints on the spatial averaging criteria by further limiting the conditions under which some areas may average measurements from multiple community-oriented monitors to determine compliance (see 71 FR 61165-61167).

^{(8)} The EPA revoked the annual PM_{10} NAAQS in 2006.