Which group of chemicals is typically emitted as gases from evaporation and contributes to air pollution?

• A. Ammonia
• B. Carbon dioxide
• C. Volatile organic compounds
• D. Methane

Answer: (C)

Gases that come from liquids evaporating are volatile organic compounds. These are organic chemicals with low boiling points, so they readily vaporize at room temperature from fuels, solvents, paints, cleaning products, and similar products. Once in the air, VOCs react in sunlight with other pollutants like nitrogen oxides to form ground-level ozone and secondary organic aerosols, which are major components of air pollution and can harm health. Ammonia, carbon dioxide, and methane come from other processes and sources, not the evaporation of everyday liquids in the same way VOCs do, so they don’t fit the scenario as directly. In short, VOCs are the gases most commonly emitted by evaporation that contribute to air pollution.