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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/m3
Not to be exceeded more than once per year
Annual 75 µg/m3 Annual Average
Secondary TSP 24-hour 150 µg/m3
Not to be exceeded more than once per year
1987

52 FR 24634
Jul 1, 1987
Primary and Secondary PM10 24-hour 150 µg/m3 Not to be exceeded more than once per year on average over a 3-year period
Annual 50 µg/m3 Annual arithmetic mean, averaged over 3 years
1997

62 FR 38652
Jul 18, 1997
Primary and Secondary PM2.5 24-hour 65 µg/m3 98th percentile, averaged over 3 years
Annual 15.0 µg/m3 Annual arithmetic mean, averaged over 3 years (3),(4)
PM10 24-hour 150 µg/m3 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/m3 Annual arithmetic mean, averaged over 3 years
2006

71 FR 61144
Oct 17, 2006
Primary and Secondary PM2.5 24-hour 35 µg/m3 98th percentile, averaged over 3 years (6)
Annual 15.0 µg/m3 Annual arithmetic mean, averaged over 3 years (2), (7)
PM10 24-hour (8) 150 µg/m3 Not to be exceeded more than once per year on average over a 3-year period
2012 Primary PM2.5 Annual 12.0 µg/m3 Annual arithmetic mean, averaged over 3 years (2), (7)
Secondary Annual 15.0 µg/m3 Annual arithmetic mean, averaged over 3 years (2), (7)
Primary and Secondary 24-hour 35 µg/m3 98th percentile, averaged over 3 years (6)
Primary and Secondary PM10 24-hour (8) 150 µg/m3 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/m3).

(2) TSP = total suspended particles.

(3)The level of the annual standard is defined to one decimal place (i.e., 15.0 µg/m3) as determined by rounding.  For example, a 3-year average annual mean of 15.04 µg/m3 would round to 15.0 µg/m3 and, thus, meet the annual standard and a 3-year average of 15.05 µg/m3 would round to 15.1 µg/m3 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/m3 would round to 35 µg/m3 and thus meet the 24-hour standard and a 3-year average of 35.50 µg/m3 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 PM10 NAAQS in 2006.

 

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