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Citizens' Guide to Air Quality in Montana

Appendix B:
Federal and State Primary Ambient Air Quality Pollutant Standards
Pollutant Time Period Federal Montana
Carbon Monoxide Hourly Average 35 ppm a 23 ppm a
8-Hour Average 9 ppm a 9 ppm a
Fluoride in Forage Monthly Average    50 mg/g b
Grazing Season    35 mg/g b
Hydrogen Sulfide Hourly Average    0.05 ppm a
Lead 90-Day Average    1.5 mg/m3 b (rolling)
Quarterly Average 1.5 mg/m3 b (calendar)   
Nitrogen Dioxide Hourly Average    0.30 ppm a
Annual Average 0.053 mg/m3 0.05 ppm b
Ozone Hourly Average 0.12 ppm c 0.10 ppm a
PM-10 (existing) 24-Hour Average 150 mg/m3 d,j 150 mg/m3 d,j
Annual Average 50 mg/m3 e 50 mg/m3 e
PM-10 (revised) 24-Hour Average 150 mg/m3 f,j   
Annual Average 50 mg/m3 e   
PM-2.5 24-Hour Average 65 mg/m3 g,j   
Annual Average 15 mg/m3 h   
Settleable Particulate 30-Day Average    10 g/m2 b
Sulfur Dioxide Hourly Average    0.50 ppm i
3-Hour Average 0.50 ppm k   
24-Hour Average 0.14 ppm j,k 0.10 ppm a,j
Annual Average 0.03 ppm k 0.02 ppm k
Visibility Annual Average   3 X 10 -5/m k
a Federal violation when exceeded more than once per calendar year.
b Not to be exceeded (ever) for the averaging time period as described in the regulation.
c Not to be exceeded more than once per year averaged over 3-years.
d Violation occurs when the expected number of days per calendar year with a 24-hour average above this concentration is more than one.
e Violation occures when the expected annual arithmetic mean concentration is above this concentration.
f To attain this standard, the 99th percentile of the distribution of the 24-hour concentrations for one year, averaged over three years, must not exceed this concentration at each monitor within an area.
g To attain this standard, the 98th percentile of the distribution of the 24-hour concentrations for one year, averaged over three years, must not exceed this concentration at each monitor within an area.
h To attain this standard, the 3-year average of the annual arithmetic mean of the 24-hour concentrations from a single or multiple population oriented monitors must not exceed this concentration.
i State violation when exceeded more than eighteen times in any 12 consecutive months.
j The standard is based upon a calendar day (midnight to midnight).
k Standard never to be exceeded during a calendar year.