Air contaminants come from a variety of sources, including industry, cars and trucks, neighborhood businesses, and fireplaces. From a public health perspective, two of the air contaminants of most concern in California are ozone and particulate matter. Ozone doesn't come from a single source, but is formed when sunlight combines with Nitrous Oxides (NOx) and Volatile Organic Compounds (VOCs). NOx comes from motor vehicle emissions, other fuel combustion, and agricultural sources. VOCs come from many sources including fossil fuels and refineries, building materials, household products including paints, and chemical manufacturing.
Exposure to air contaminants is linked to many distinct health conditions including respiratory disease and cardiovascular disease.
To track air quality in California we use information about the amount of air contaminants known to be harmful to human health. In our data query, we display information on two indicators: ozone and PM2.5 (particulate matter smaller than 2.5 microns). We provide the option of displaying: 1) the concentration of these contaminants and 2) the number of days that exceed regulatory standards. The regulatory standards are set by the Environmental Protection Agency and California Air Resource Board at levels related to their impact on human health.