Air Quality Monitoring Data
Summary Particulate Matter 2.5 (PM2.5)
The EPA established a health based standard (National Ambient Air Quality Standard, (NAAQS)) for fine particulate matter (PM2.5), which is a byproduct of combustion. The 24 hour PM2.5 standard is based on the 98th percentile averaged over 3 years. The interactive chart below shows the 98th percentiles and design values as measured since 2000 at the Butte and Palmer air monitoring stations. The Palmer site was shut down in 2019. An area is in violation of the NAAQS when the Design Value is greater than the 24 hour NAAQS for PM2.5, which is currently set at 35 µg/m3.
Note: The vertical axis of this chart extends to 100 µg/m3. The PM2.5 concentrations represent the concentration at local conditions and have not been corrected for local temperature and pressure
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 (PM2.5 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 PM2.5 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 PM2.5 exceeds the NAAQS.
- 98th Percentile
- The daily value out of a year of PM2.5 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 PM2.5, 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 PM2.5 NAAQS
- 24-Hour: 98th 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
| Standard | 1997 - 2006 | 2006 - 2012 | 2012 - 2024 | 2024 - current |
|---|---|---|---|---|
| 24-hour | 65 µg/m3 | 35 µg/m3 | 35 µg/m3 | 35 µg/m3 |
| Annual | 15 µg/m3 | 15 µg/m3 | 12 µg/m3 | 9 µg/m3 |