Air Pollutants
The EPA uses six so-called Òcriteria pollutantsÓ to assess air quality.
Those are: Ozone (O3), Carbone Monoxide(CO), Nitrogen Dioxide(NO2), Sulfur Dioxide (SO2),
Particulate Matter (PM) and Lead.
Maximum values not be exceeded more than once per year over 1, 3, 8 and/or 24 hour periods have been defined
and are the basis for the Air Quality Index (AQI) used for pollution forecasting and public service announcements.
It should be noted that those "maximum values" have been defined differently over the past 30 years.
The table below represents current guidelines used by the EPA:
| Ozone | .12 ppm over 1 hour period. .092 ppm over 8-hour period. |
| Carbon Monoxide | 35 ppm over 1 hour period. 9 ppm over 8-hour period. |
| Nitorgen Dioxide | .053ppm 3-hour period |
| Sulfur Dioxide | .5ppm over 3-hour period |
| Particulate Matter (PM2.5) | 15 micro-grams per cubic meter over 24-hour period. |
| Particulate Matter (PM10) | 50 micro-grams per cubic meter over 24-hour period. |
For more detailed information, please look at the EPA's website: https://www.epa.gov/green-book
