Which gas is released through evaporation or incomplete combustion of fossil fuels and other organic chemicals?

• A. Ozone
• B. Secondary Pollutant
• C. Volatile Organic Compound (VOC)
• D. Primary Pollutant

Answer: (C)

Volatile organic compounds are gases or vapors of organic chemicals that readily escape into the air because they have high vapor pressures. When fuels, solvents, paints, and other organic liquids evaporate, they release VOCs directly into the atmosphere. They also appear in emissions from incomplete combustion of fossil fuels. Because VOCs are emitted directly from sources into the air, they are considered primary pollutants. At the same time, VOCs can react with nitrogen oxides in the presence of sunlight to form ozone, a secondary pollutant, but the question describes the actual emitted gas from evaporation or incomplete combustion, which is VOC. Ozone is not released directly; it forms later in the atmosphere. A secondary pollutant is a pollutant produced by chemical reactions, not released as such, and a primary pollutant is a broad category for pollutants emitted directly, with VOCs being a specific example.