Air quality is continuously monitored throughout the San Diego Air Basin, however since population and most pollution sources are concentrated in the western portion of the county, the District conducts its air sampling at ten monitoring stations in the western region. District technicians and chemists continuously maintain and operate sophisticated electronic analyzers and sensors at the monitoring stations to determine the type and level of pollutants in the outside air. District meteorologists use data collected from the monitoring stations to assess the county’s air quality status and forecast daily pollution levels.