Air Trends

Nitrogen Dioxide Trends

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National Trends in Nitrogen Dioxide Levels

Using a nationwide network of monitoring sites, EPA has developed ambient air quality trends for nitrogen dioxide (NO2). Under the Clean Air Act, EPA sets and reviews national air quality standards for NO2. Air quality monitors measure concentrations of NO2 throughout the country. EPA, state, tribal and local agencies use that data to ensure that NO2 in the air is at levels that protect public health and the environment. Nationally, average NO2 concentrations have decreased substantially over the years. For information on NO2 standards, sources, health effects, and programs to reduce NO2, please see
How to Interpret the Graphs



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Regional Trends in Nitrogen Dioxide Levels

Air quality trends can vary regionally. The following climatically consistent regions within the contiguous United States provide a relevant way to look at regional trends in air quality.

U.S. Climate Regions from NOAA's National Climatic Data CenterSource: NOAA National Climatic Data CenterSelect a region: (graph appears below)

Note: The Northwest region does not have enough data to construct a regional trend for nitrogen dioxide.


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