A list of air pollutants discharged into the atmosphere over a period, typically a year. Inventories can exist for a variety of entities, including companies, industry groups (e.g., OGCI, ONE Future), basins, and countries. Inventories are often broken into source categories, which may be general (e.g., venting versus fugitives) or granular (e.g., high-bleed versus low-bleed pneumatics).