I have little doubt that the list of toxic substances has grown, and tolerable levels dropped (how clean is clean?)
J
ust to demonstrate the moving goalposts the EPA establishes, look at the historical limits of particulates.
How can anyone forecast how to be within the arbitrary limits?https://www.epa.gov/pm-pollution/timeline-particulate-matter-pm-national-ambient-air-quality-standards-naaqsTimeline of Particulate Matter (PM) National Ambient Air Quality Standards (NAAQS)
History of the NAAQS for Particulate Matter, from 1971 to 2024
Final Rule/Decision Primary/Secondary Indicator1 Averaging Time Level2 Form
1971
36 FR 8186
Apr 30, 1971 Primary TSP 24 hour 260 µg/m3 Not to be exceeded more than once per year
1971
36 FR 8186
Apr 30, 1971 Primary TSP Annual 75 µg/m3 Annual geometric mean
1971
36 FR 8186
Apr 30, 1971 Secondary TSP 24 hour 150 µg/m3 Not to be exceeded more than once per year
1971
36 FR 8186
Apr 30, 1971 Secondary TSP Annual 60 µg/m3 Annual geometric mean
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
1987
52 FR 24634
Jul 1, 1987 Primary and Secondary PM10 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
1997
62 FR 38652
Jul 18, 1997 Primary and Secondary PM2.5 Annual 15.0 µg/m3 Annual arithmetic mean, averaged over 3 years 3, 4
1997
62 FR 38652
Jul 18, 1997 Primary and Secondary 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
1997
62 FR 38652
Jul 18, 1997 Primary and Secondary PM10 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
2006
71 FR 61144
Oct 17, 2006 Primary and Secondary PM2.5 Annual 15.0 µg/m3 Annual arithmetic mean, averaged over 3 years 2, 7
2006
71 FR 61144
Oct 17, 2006 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
2012
78 FR 3085
Jan 15, 2013 Primary PM2.5 Annual 12.0 µg/m3 Annual arithmetic mean, averaged over 3 years 2, 7
2012
78 FR 3085
Jan 15, 2013 Secondary PM2.5 Annual 15.0 µg/m3 Annual arithmetic mean, averaged over 3 years 2, 7
2012
78 FR 3085
Jan 15, 2013 Primary and Secondary PM2.5 24 hour 35 µg/m3 98th percentile, averaged over 3 years 6
2012
78 FR 3085
Jan 15, 2013 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
2020
85 FR 82684 Dec 18, 2020
Primary and secondary standards retained, without revision.
2024 Primary PM2.5 Annual 9.0 µg/m3 Annual arithmetic mean, averaged over 3 years 2, 7
2024
Secondary PM2.5 standards, and primary and secondary PM10 standards, retained without revision.
1. TSP = Total Suspended Particles
2. Units of measure are micrograms per cubic meter of air (µg/m3).
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.
