DEQ is required to conduct air quality monitoring by both federal and state regulations. The air sampling program is a combined effort of the Air Quality Monitoring Office (AQM), six regional offices, the Alexandria Transportation and Environmental Services, the National Park Service, and the US Department of Agriculture Forest Service. DEQ regional, locality, and federal operators routinely service the monitoring instrumentation, perform the quality assurance checks necessary to ensure that the analyzers are operating properly, and perform various types of preventive maintenance. This instrumentation at air monitoring sites scattered across Virginia measure the ambient air for the criteria pollutants and other air pollutants of special interest using methods and procedures approved by the U.S. Environmental Protection Agency (EPA). This ensures all recorded data are complete, precise, accurate, representative, and comparable.

Air quality measurements are taken on the following "criteria pollutants": CO, O3, SO2, NO2, PM10 (particulate with an aerodynamic diameter less than or equal to 10 microns in size), and PM 2.5 (particulate with an aerodynamic diameter less than or equal to 2.5 microns in size). Some additional sampling is conducted for volatile organic compounds, also known as the "ozone precursors." Sampling sites are located across the Commonwealth, but tend to be concentrated in more populated areas.

The EPA has specific requirements for a minimum number of monitoring sites, called NAMS - National Air Monitoring Sites, and Virginia has augmented these with additional sites, called SLAMS - State & Local Air Monitoring Sites, to provide additional air quality data for DEQ needs. Specific locations of these monitoring sites are determined by factors such as population density, emissions sources, permitting needs, modeling results, and site accessibility.