The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (40 CFR part 50) for pollutants considered harmful to public health and the environment. The Clean Air Act identifies two types of national ambient air quality standards. Primary standards provide public health protection, including protecting the health of “sensitive” populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.
The EPA has set National Ambient Air Quality Standards for six principal pollutants, which are called “criteria” air pollutants. Periodically, the standards are reviewed and may be revised. The current standards are listed below. Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3).
[links to historical tables of NAAQS reviews]
|Carbon Monoxide (CO)||primary||8 hours||9 ppm||Not to be exceeded more than once per year|
|1 hour||35 ppm|
|Lead (Pb)||primary and
|Rolling 3 month average||0.15 μg/m3 (1)||Not to be exceeded|
|Nitrogen Dioxide (NO2)||primary||1 hour||100 ppb||98th percentile of 1-hour daily maximum concentrations, averaged over 3 years|
|1 year||53 ppb (2)||Annual Mean|
|Ozone (O3)||primary and
|8 hours||0.070 ppm (3)||Annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years|
|Particle Pollution (PM)||PM2.5||primary||1 year||12.0 μg/m3||annual mean, averaged over 3 years|
|secondary||1 year||15.0 μg/m3||annual mean, averaged over 3 years|
|24 hours||35 μg/m3||98th percentile, averaged over 3 years|
|24 hours||150 μg/m3||Not to be exceeded more than once per year on average over 3 years|
|Sulfur Dioxide (SO2)||primary||1 hour||75 ppb (4)||99th percentile of 1-hour daily maximum concentrations, averaged over 3 years|
|secondary||3 hours||0.5 ppm||Not to be exceeded more than once per year|
(1) In areas designated nonattainment for the Pb standards prior to the promulgation of the current (2008) standards, and for which implementation plans to attain or maintain the current (2008) standards have not been submitted and approved, the previous standards (1.5 µg/m3 as a calendar quarter average) also remain in effect.
(2) The level of the annual NO2 standard is 0.053 ppm. It is shown here in terms of ppb for the purposes of clearer comparison to the 1-hour standard level.
(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 an implementation plan providing for attainment of the current (2010) standard has 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 required NAAQS.
Nonattainment Status for Indiana Counties
Specific nonattainment history for each of the criteria pollutants for the State of Indiana is provided here by the Indiana Department of Environmental Management (IDEM): https://www.in.gov/idem/airquality/2339.htm