National Ambient Air Quality Standards
|Pollutant||Primary/ Secondary||Averaging Time||Level||Form|
|Carbon Monoxide||primary||8-hour||9 ppm||Not to be exceeded more than once per year|
|Lead||primary and secondary||Rolling 3-month average||0.15 µg/m3 (1)||Not to be exceeded|
|Nitrogen Dioxide||primary||1-hour||100 ppb||98th percentile of 1-hour daily maximum concentrations, averaged over 3 years|
|primary and secondary||Annual||53 ppb (2)||Annual Mean|
|Ozone||primary and secondary||8-hour||0.070 ppm (3)||Annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years|
|Particle Pollution||PM2.5||primary||Annual||12 µg/m3||annual mean, averaged over 3 years|
|secondary||Annual||15 µg/m3||annual mean, averaged over 3 years|
|primary and secondary||24-hour||35 µg/m3||98th percentile, averaged over 3 years|
|PM10||primary and secondary||24-hour||150 µg/m3||Not to be exceeded more than once per year on average over 3 years|
|Sulfur Dioxide||primary||1-hour||75 ppb (4)||99th percentile of 1-hour daily maximum concentrations, averaged over 3 years|
|secondary||3-hour||0.5 ppm||Not to be exceeded more than once per year|
(1) Final rule signed October 15, 2008. The 1978 lead standard (1.5 µg/m3 as a quarterly average) remains in effect until one year after an area is designated for the 2008 standard, except that in areas designated nonattainment for the 1978 year, the 1978 standard remains in effect until implementation plans to attain or maintain the 2008 standard are approved.
(2) The official level of the annual NO2 standard is 0.053 ppm, equal to 53 ppb, which is shown here for the purpose of clearer comparison to the 1-hour standard.
(3) Final rule signed October 1, 2015, and effective December 28, 2015. The previous (2008) O3 standards additionally remain in effect in some areas. Revocation of the previous (2008) O3 standards and transitioning to the current (2015) standards will be addressed in the implementation rule for the current standards.
(4) The previous SO2 standards (0.14 ppm 24-hour and 0.03 ppm annual) will additionally remain in effect in certain areas: (1) any area for which it is not yet 1 year since the effective date of designation under the current (2010) standards, and (2) any area for which implementation plans providing for attainment of the current (2010) standard have not been submitted and approved and which is designated nonattainment under the previous SO2 standards or is not meeting the requirements of a SIP call under the previous SO2 standards (40 CFR 50.4(3)), A SIP call is an EPA action requiring a state to resubmit all or part of its State Implementation Plan to demonstrate attainment of the require NAAQS.