The Air Facilities data in LandView is extracted from the Aerometric Information Retrieval System (AIRS) and maintained by the Office of Air and Radiation. AIRS stores information from the 50 states on air quality, point source emissions, and area/mobile source data required by federal regulation. This monitoring is required for criteria pollutants (identified through the Clean Air Act) and is based on population, pollutant sources, geographical area, etc. Point sources emitting more than 100 tons per year of any criteria pollutant (except 5 tons per year for lead and 1000 tons per year for carbon monoxide) must report actual or estimated annual emissions data. Data in the system is available to the public through agency publications in NTIS. LandView III uses the symbol "A" when displaying air facilities.