Definition

Primary pollutants are air pollutants emitted directly into the atmosphere from identifiable natural or human-made sources. These pollutants are released directly into the air rather than being formed through chemical reactions in the atmosphere. They originate from sources such as vehicles, industrial facilities, power plants, construction activities, fires, and natural processes. Examples include particulate matter (PM), sulfur dioxide (SO₂), nitrogen oxides (NOₓ), carbon monoxide (CO), and lead (Pb). Some primary pollutants also participate in atmospheric reactions and contribute to the formation of secondary pollutants.