Final answer:
Primary pollutants are released directly into the air, while secondary pollutants are formed through reactions between primary pollutants and atmospheric compounds.
Step-by-step explanation:
Pollutants are categorized into two major types based on how they originated namely primary and secondary pollutants. Primary pollutants are those released directly from the source into the air in a harmful form. The primary pollutants that account for nearly all air pollution problems are carbon monoxide, volatile organic compounds (VOCs), nitrogen oxides, sulfur dioxides, and particulate material. Secondary pollutants are produced through reactions between primary pollutants and normal atmospheric compounds.