About Air Quality

Air is the most precious of resources - our lives depend on it. It is made up of 78 percent nitrogen, 21 percent oxygen, and less than one percent gases like argon and carbon dioxide. Unfortunately, it can also contain substances that are unhealthy for us to breathe...

Air Quality Status

Sources of Air Pollution

In the Bay Area, a certain amount of air pollution comes from industrial sources, such as refineries and power plants. But a greater percentage of harmful air emissions comes from cars and trucks, construction equipment, and other motor vehicles. In the wintertime, the largest single source of air pollution is residential wood burning.

  • Spare the Air
    Learn about the Spare the Air Program, how the seasons affect air quality, and how to find out whether a Spare the Air Alert is in effect.
  • Wood Smoke Pollution
    Learn how the Air District is reducing wood smoke pollution in the Bay Area through Winter Spare the Air Alerts and restrictions on wood burning, and find out how you can help at home.

Types of Air Pollution

In order to protect public health, the U.S. EPA and the state of California have created air quality standards for pollutants that are commonly present in the air we breathe.

In the Bay Area, the common pollutants of greatest concern are ozone and fine particulate matter. Ozone is the main ingredient in summertime smog, and fine particulate matter - which is made up of an assortment of extremely small airborne particles, or mixtures of solid particles and liquid droplets - is primarily a problem in the wintertime.

The state of California has also identified a category of air pollutants called toxic air contaminants. These are generally present in very small amounts in the air, but are extremely hazardous to human health. In the Bay Area, the toxic air contaminant of greatest overall concern is exhaust from diesel engines.

To learn more about these and other pollutants in the Bay Area you can use the Pollutant Glossary.

  • Air Quality Summary Reports
    View annual reports summarizing the air quality data collected from the Bay Area's air quality monitoring network.
  • Air Quality Monitoring
    Learn about the Air District’s air monitoring program and its activities, including the air monitoring network, the laboratory, and pollutant source testing.

Greenhouse gases

There is another important category of substances emitted into the air called greenhouse gases (GHG). Many of these are not harmful to breathe, but cause the atmosphere to retain heat in the process called climate change. The most common greenhouse gases are carbon dioxide and methane.

Learn how the Air District’s Climate Protection program is working to reduce GHG emissions.

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General Information


Meteorology & Measurements
Air Monitoring


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Spare the Air Status

Last Updated: 12/12/2016