Form in the atmosphere from primary pollutants?

• A. Ozone
• B. Primary pollutants
• C. Particulate matter
• D. Secondary pollutants

Answer: (D)

Secondary pollutants are substances formed in the atmosphere through chemical reactions of primary pollutants. When pollutants like nitrogen oxides, sulfur dioxide, and volatile organic compounds are released, they can react in sunlight and with other atmospheric components to create new pollutants, rather than being emitted directly.

This is why the concept fits: ozone, for example, is not emitted as a gas from sources but forms in the air from precursors under sunlight. Particulate matter can be either primary (emitted directly) or secondary (produced from gas-phase precursors). So the category defined by “formed in the atmosphere from primary pollutants” is secondary pollutants.