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Air Quality Data Assessment and Analysis

Individuals who breathe polluted air can experience health effects within a few hours or days. EPA established national ambient air quality standards for certain common pollutants to protect public health. The District predicts air quality on a daily or seasonal basis so that individuals can anticipate and respond on days when the air standards are exceeded. Trends are observed over time to assess improvements in overall air quality.

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Air Quality Forecasts

The District predicts air quality using historic monitoring data and surface meteorological conditions for the Air Quality Index (AQI), a color-coded forecasting tool used to communicate pollution levels and related health effects to the public. The AQI is based on concentration levels of five major pollutants regulated under the Clean Air Act: ground-level ozone, particulate matter; carbon monoxide, sulfur dioxide and nitrogen dioxide. The daily forecasts focus on the air pollutant likely to reach the highest AQI level on a given day. Air quality alerts are distributed to the public on days when pollution levels are expected to be high, such as on "Code Red" days. Most high AQI levels in the DC metropolitan region are due to ground-level ozone, the main component of smog. Smog is formed on hot sunny days with little wind when nitrogen oxides and volatile organic compounds, emitted from vehicles and other sources, are in the proper conditions to "cook" in the presence of sunlight.

photo of air quality monitoring station

Air Quality Trends

The District determines the effectiveness of air quality regulations using the results of monitoring data over time. Rising pollution levels generally indicate that more controls are necessary, whereas a drop in pollution levels demonstrate that existing controls are successfully reducing emissions. This information is incorporated into air quality planning.


Service Contact: 
Rama Tangirala
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