District Air Monitor Sites

The District maintains a database of air quality data collected at ambient air monitoring locations located throughout the region. Monitored pollutants include Ozone (O3), Oxides of Nitrogen (NO and NO2), Carbon Monoxide (CO), Sulfur Dioxide (SO2), Hydrogen sulfide (H2S), Particulate Matter (PM10 and PM2.5), hydrocarbons, elemental and organic carbon, and various hazardous air pollutant compounds. Monitoring locations must meet a strict set of site selection guidelines.

Click on the dots to view location and pollutant monitoring details for air monitoring stations in operation since 2000. Tables of hourly data from the District's current ambient air monitoring network stations are also available.

Monitoring Site Selection Guidelines
Monitoring sites for regional gaseous pollutants such as ozone (O3), oxides of nitrogen (NO and NO2), and carbon monoxide (CO) are selected based on population exposure and at locations with the highest expected concentrations. Some pollutants such as sulfur dioxide (SO2), hydrogen sulfide (H2S), and hydrocarbons are closely associated with a particular type of industry and so monitoring locations are typically placed near these industrial sources. Other pollutants can be a hybrid of these two types, having a regional aspect with particular sources identified with them. Particulate matter (PM10 and PM2.5) and toxics pollutants fall into this category and are sited to provide regional coverage and/or located near potential sources. The District must follow strict guidelines issued by the EPA and the State of California to ensure accuracy and uniformity. Sites are also located where they can be operated for long periods of time, with the minimum usually being a year, to provide information regarding seasonal variations in pollutant concentrations.