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Outdoor Air

Tracking Air Quality

Federal, state, local, and tribal air agencies operate and maintain a wide variety of outdoor air monitoring systems across the United States. Many of these systems serve several environmental objectives. At a basic level, they let us know how clean or polluted the air is, help us track progress in reducing air pollution, and inform the public about air quality in their communities through the Air Quality Index (AQI). The AQI is a tool to help you quickly learn when air pollution is likely to reach unhealthy levels.

Air Quality System Database

The Air Quality System (AQS) database contains ambient air pollution data. The data are collected by EPA and state, local, and tribal air pollution control agencies. The United States has approximately 4,000 monitoring stations, mainly in urban areas. AQS also contains meteorological data, information about each monitoring station such as its location and its operator, and data quality assurance and quality control information.

Smoke stacks of a US factoryAQS is important because it helps EPA and others to

  • assess air quality,
  • assist in determining which areas of the country are meeting air quality standards,
  • evaluate state plans for controlling air pollution,
  • perform modeling for permit review analysis, and
  • perform other air quality analyses such as trend analysis and health effect studies.

AQS information is also used to prepare reports for Congress, as required by the Clean Air Act.

CDC's tracking program is working with EPA to produce air quality indicators in areas without air monitors. These indicators are produced by combining air monitoring data with emissions and meteorological data to create daily estimates of ozone and airborne fine particulates. This process helps construct a more complete picture of air pollution across the country. Read more about monitor and modeled data.

National-Scale Air Toxics Assessment

The National-Scale Air Toxics Assessment (NATA) is EPA's ongoing comprehensive evaluation of air toxics in the U.S. Data from this system are used to calculate the Air Toxics indicators for benzene and formaldehyde that are available on the Tracking Network. According to EPA, the NATA assessments were designed to help guide efforts to cut toxic air pollution and build upon the already significant emissions reductions achieved in the US since 1990.

NATA was developed as a tool to inform both national and more localized efforts to collect air toxics information, characterize emissions, and help prioritize pollutants/geographic areas of interest for more refined data collection and analyses. The goal is to identify those air toxics which are of greatest potential concern in terms of contribution to population risk.

Read specific air quality indicators information:

A nature shot with a bird sitting on a dead tree and a deer in the background

Ozone - Days Above Regulatory Standard
(Monitor + Modeled)  (Monitor only)

The number of days in which the daily maximum 8-hour average ozone concentration exceeds a standard provides an indication of short-term spikes in ozone concentrations. This may give you an idea of how many days per year you may be exposed to unhealthy levels of ozone.

PM2.5 - Days Above Regulatory Standard
(Monitor + Modeled)  (Monitor only)

These data help summarize short-term trends in particle pollution concentrations. This may give you an idea of how many days per year you may be exposed to unhealthy levels of particulate matter.

Annual PM2.5 Level
(Monitor + Modeled)  (Monitor only)

These data help summarize long-term trends in particle pollution concentrations. This will give you an idea of what the yearly level of PM2.5 is in an area.

Mortality Benefits associated with Reducing PM2.5 concentration levels

These data summarize the estimated number of deaths prevented and percent change in deaths associated with lowering PM2.5 concentration levels.

Air Toxics

Air toxics measures can be used to prioritize emission sources as potential targets for risk reduction activities and further study, identify locations of interest for further investigation, and show the geographic distribution of air toxics. These measures are based on modeling data alone and should not be used as a sole means for identifying localized hotspots or to compare risks at local levels such as between neighborhoods.

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