The National Emission Inventory contains measured, modeled, and estimated data for emissions of all known source categories in the US (stationary sources, fires, light duty vehicles and trucks, Heavy duty engines, Motorcycles, ATVs, non-road engines and equipment, locomotives, aircraft, and marine vessels). The statutory authority leading to the collection of this information comes from Title II, Part A of the Clean Air Act.Substance classes include CAPs, HAPs, and some GHG data.Data included in the National Emission Inventory is collected annually, Air Pollutant Trends Data is made available annually, and an National Emissions Inventory of air emissions of both Criteria and Hazardous air pollutants from all air emissions sources is prepared every three years.