Secondary pollutants are pollutants that are not directly emitted into the atmosphere, but are formed when primary pollutants react with other substances in the air. These reactions can occur through chemical reactions, interaction with sunlight, or other atmospheric processes. Some common secondary pollutants include ozone, smog, and fine particulate matter. Unlike primary pollutants, which are directly emitted from sources like vehicles and factories, secondary pollutants can be more challenging to control because they are formed through complex chemical reactions in the atmosphere.
