Table 1. AMBIENT AIR QUALITY STANDARDS 

Standards 

Air Contaminants (Maximum Permissible Concentrations) 

lnhalable 150 micrograms per cubic meter, 24-hour average 

concentration. The standard is attained when the 

expected number of days per calendar year with a 

24-hour average concentration above 150 micrograms 

per cubic meter, as determined in accordance with 40 

CFR 50, Appendix K, is equal to or less than one. 

Particulates 

PM10 

PM 2.5 

Sulfur 

Dioxide 

Hydrogen 

Sulfide 

Carbon 

Monoxide 

12.0 micrograms per cubic meter annual arithmetic mean 

concentration. The standard is met when the annual 

arithmetic mean concentration, as determined in 

accordance with 40 CFR 50, Appendix N, is less than 

or equal to 12.0 micrograms per cubic meter. 

35 micrograms per cubic meter 24-hour average 

concentration. The standard is met when the 9sth 

percentile 24-hour concentration, as determined in 

accordance with 40 CFR 50, Appendix N, is less than 

or equal to 35 micrograms per cubic meter. 

0.075 parts per million (196 micrograms per cubic meter) 

1-hour average concentration. The standard is met 

when the 3-year average of the annual 99th percentile 

of the daily maximum 1-hour average concentration 

is less than or equal to 0.075 parts per million, as 

determined in ac~ordance with 40 CFR 50, Appendix T. 

0.5 parts per million (1309 micrograms per cubic meter of 

air) maximum 3-hour concentration, not to be exceeded 

more than once per calendar year. 

10.0 parts per million (14 milligrams per cubic meter of air), 

maximum instantaneous (ceiling) concentration not to 

be exceeded 

·0.20 parts per million (280 micrograms per cubic meter of 

air), maximum 1-hour average concentration not to be 

exceeded more than once per month 

0.10 parts per million (140 micrograms per cubic meter of 

air), maximum 24-hour average concentration not to be 

exceeded more than once per year 

0.02 parts per million (28 micrograms per cubic meter of air), 

maximum arithmetic mean concentration averaged over 

three consecutive months 

9 parts per million (1 O milligrams per cubic meter of air), 

maximum 8-hour concentration not to be exceeded 

more than once per year 

4 
Ozone 

Nitrogen 

Dioxide 

Lead 

35 parts per million (40 milligrams per cubic meter of air), 

maximum 1-hour concentration not to be exceeded 

more than once per year 

0.075 parts per million (147 micrograms per cubic meter of 

air) daily maximum 8-hour average concentration. The 

standard is met when the three-year average of the 

annual fourth-highest daily maximum 8-hour average 

concentration at an ambient air quality monitoring site 

is less than or equal to 0.075 ppm, as determined in 

accordance with 40 CFR 50, Appendix P. 

0.053 parts per million (100 micrograms per cubic meter of 

air), maximum annual arithmetic mean 

0.100 parts per million (188 micrograms per cubic meter) 

1-hour average concentration. The standard is met 

when the 3-year average of the annual 98th percentile 

of the daily maximum 1-hour average concentration 

is less than or equal to 0.100 parts per million, as 

determined in accordance with 40 CFR 50, Appendix S. 

0.15 micrograms per cubic meter of air, arithmetic mean 

averaged over a 3-month rolling period. The standard is 

met when the maximum 3-month mean concentration 

for a 3-year period, as determined in accordance 

with 40 CFR 50, Appendix R, is less than or equal to 

0.15 micrograms per cubic meter. 

History: Amended effective December 1, 1994; April 1, 2009; April 1, 2011; April 

1, 2014.