Which pollutant forms in the atmosphere from primary pollutants?

• A. Ozone
• B. Primary pollutants
• C. Secondary pollutants
• D. Aerosols

Answer: (C)

Secondary pollutants form in the atmosphere from reactions of primary pollutants. Primary pollutants are emitted directly into the air, such as exhaust, smoke, and dust. When these emissions interact in the air—often driven by sunlight, temperature, and humidity—they can transform into new substances. Ozone at ground level is a classic example, created through photochemical reactions involving nitrogen oxides and volatile organic compounds in sunlight. Other secondary pollutants include sulfates and nitrates that form when sulfur dioxide and nitrogen oxides react and condense into particulate matter. Because the question asks for the pollutant formed in the atmosphere from primary pollutants, the correct concept is the category of secondary pollutants.