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/ / / / NAAQS Info and Non-Attainment

NAAQS Info and Non-Attainment

The Clean Air Act (CAA) is the comprehensive federal law that regulates air emissions from stationary and mobile sources. Among other things, this law authorizes the EPA to establish the National Ambient Air Quality Standards (NAAQS) to protect public health and welfare and to regulate emissions of hazardous air pollutants.


The Clean Air Act was last amended in 1990 and requires the EPA to set National Ambient Air Quality Standards (NAAQS) for wide-spread pollutants from numerous and diverse sources considered harmful to public health and the environment. The Clean Air Act established two types of (NAAQS).  Primary standards set limits to protect public health, and Secondary standards set limits to protect public welfare. The Clean Air Act requires periodic review of the science upon which the standards are based and to revise the standard as dictated by the scientific analysis.


EPA defines an area or county meeting a given NAAQS standard as an "attainment area" for that standard.  If it doesn't meet the standard, it is designated as a "non-attainment area".


The statements and/or data contained on this Web Site are for informational purposes only and not represented to be error free.  While every effort is made to ensure this information is up-to-date and accurate, official information can be found on the Web sites of the US Environmental Protection Agency, California Air Resources Board and/or other appropriate regulatory agencies.  This Web Site should not be used as a substitute for competent legal advice from a licensed professional attorney in your state or jurisdiction.

National Ambient Air Quality Standards
Criteria PollutantPrimary or SecondaryTime PeriodLevel
Nitrogen Dioxide (NO2) Primary 1-Hour 100 ppb
Nitrogen Dioxide (NO2) Primary & Secondary Annual 53 ppb
Ozone (O3) Primary & Secondary 8-Hour 70 ppb
Particle Pollution PM2.5 Primary & Secondary annual 15 ug/m3
Particle Pollution PM2.5 Primary & Secondary 24-Hour 35 ug/m3
Particle Pollution PM10 Primary & Secondary 24-Hour 150 ug/m3
Carbon Monoxide (CO) Primary 8-Hour 9 ppb
Carbon Monoxide (CO) Primary 1-Hour 35 ppb
Lead Primary & Secondary Rolling 3 Month Average .15 ug/m3
Sulfur Dioxide (SO2) Primary 1-Hour 75 ppb
Sulfur Dioxide (SO2) Secondary 3-Hour .5 ppm

Nitrogen Dioxide (NO2)

Nitrogen dioxide (NO2) is one of a group of highly reactive gasses known as "oxides of nitrogen," or "nitrogen oxides (NOx)."   NO2 can be formed

naturally by lightening strikes, from plants and soil, however it is also formed through  the internal combustion process that uses air as the oxidant. 

On September 22, 2012, the EPA adopted a new 1-hour NO2 standard at  the level of 100 parts per billion and retained the existing annual NO2 standard
of 53 ppb.

A key part of the new 1-hour standard is the new ambient air monitoring network and reporting requirement:

  • In urban areas, monitors are required near major roads and areas where major concentrations are expected
  • Additional monitors are required in large urban areas to measure areas with the highest NO2 concentrations
  • The new monitoring system must be in place and fully compliant by 2013
  • The first non-attainment designations for the 1-hour standard (with a compliant monitoring system) will be in the 2016 to 2017 timeframe.


EPA Nitrogen Dioxide (NO2) Home Page: 

Regulatory Actions: 

Non-Attainment Designations: 

Non-Attainment Information by State: 

Ozone (O3)

Ozone is found in two regions of the Earth's atmosphere, in the upper regions where it prevents damaging ultraviolet light

from reaching the Earth's surface, and ground level .  Both ground level and upper region ozone has the same chemical
composition of (O3).

  • Ozone is caused by the interaction of sunlight and nitrogen oxides
  • When nitrogen oxide is present in the air, and sunlight hits the nitrogen oxide, this results in the creation of ozone


The 8-hour ozone standard was last revised October, 2015 from 75 to 70 parts per billion. EPA projects that the revision will result in a total of 241 non-attainment counties. The EPA communicated the following timing of the revision:

  • Final nonattainment designations will be made in 2017 most likely based on 2014-2016 air quality monitoring
  • Any states designated nonattainment from this revision must achieve attainment in the 2020 to 2037 timeframe


EPA Ozone (O3) Home Page: 

Regulatory Actions: 

Non-Attainment Designations: 

Particle Pollution PM2.5

Particulate matter is a term used to describe a mixture of a complex group of fine airborne solid particles and liquid droplets (aerosols) which includes components of nitrates, sulfates, elemental carbon, organic carbon compounds, acid aerosols, trace metals, and geological material. 

EPA has developed two PM standard categories:

  • PM10 which are particles with a diameter smaller that 10 micrometers and larger than 2.5 micrometers  and are known as "Inhalable coarse particles," such as those found near roadways and dusty industries
  • PM2.5 which are particles with a diameter smaller than 2.5 micrometers and are known as "Fine particles“


On December 14th, 2012 the EPA concluded a revision of the PM2.5 fine particle standard.  The results of the revision include:

  • Retained the 24-hour standard at 35 ug/m3. This was last revised in 2006.
  • Strengthen the annual fine particle standard from 15 down to 12 ug/m3
    • EPA modeling projects/estimates this revision will result in 66 non-attainment counties, however they will utilize a two-year review process and will finalize non-attainment designations by December, 2014.
    • Adds a “heavily traveled road in large urban areas” monitor requirement which will require the re-location of 52 of the existing 900 monitors.
    • The 12 ug/m3 standard is to be met by 2020, however states can request and an additional 5-year extension.
  • State implementation plans (SIPs) are due 2018 that outline the steps that each state (in nonattainment) will take to meet the standard.


EPA Particulate Matter Home Page: 

Regulatory Actions: 

Non-Attainment Designations: