Division of Air Quality Monitoring and Quality Assurance

Glossary

NAAQS

National Ambient Air Quality Standard - A health-based air quality standard set by EPA based on a review of available scientific information. NAAQS exist for criteria pollutants including Particulate Matter (PM_2.5 and PM₁₀), Carbon Monoxide (CO), Sulfur Dioxide (SO₂), Nitrogen Dioxide (NO₂), Ozone(O₃), and Lead(Pb).

EPA's NAAQS Webpage

Concentration, µg/m³

The amount of PM_2.5 suspended in the air with units of micrograms(one-millionth of a gram) per cubic meter

Exceedance

A day when the 24-hour measured concentration of PM_2.5 exceeds the NAAQS.

98^th Percentile

The daily value out of a year of PM_2.5 monitoring data below which 98 percent of all daily values fall. 40 CFR 50 Appendix N - see section 4.5(a)

24-hour Design Value (DV)

A three-year average of the 98th percentile value. An area is in violation of the NAAQS when the Design Values is greater than the 24-hour NAAQS for PM_2.5, which is currently set at 35 µg/m³40 CFR 50 Appendix N - see section 4.5(b)

Clean Data Year

A year when the 98th percentile value is less than the NAAQS.

Exceptional Events

Unusual or naturally occurring events that can affect air quality but are not reasonably controllable.

EPA's Exceptional Events Webpage

DEC's Exceptional Events Webpage

Compliance with PM_2.5 NAAQS

24-Hour: 98^th percentile, averaged over 3 years, must be below the standardAnnual: Annual arithmetic mean, averaged over 3 years, must be below the standard. 40 CFR 50 Appendix N - see sections 4.1 and 4.2