Which of the following is a major primary pollutant?

• A. Ozone
• B. Lead
• C. Particulate Matter
• D. Nitric Acid

Answer: (C)

Primary pollutants are substances released directly into the air from a source, rather than forming later through chemical reactions in the atmosphere. Ozone isn’t released directly; it forms when sunlight drives chemical reactions among nitrogen oxides and volatile organic compounds, so it’s a secondary pollutant. Nitric acid also forms after emissions mix with atmospheric chemistry, so it’s not a primary pollutant either. Particulate matter, on the other hand, is emitted directly as tiny solid particles or liquid droplets from sources like vehicle exhaust, industrial processes, burning, and dust. Because these particles are released straight into the air and have widespread health and environmental impacts, particulate matter is classified as a major primary pollutant. Lead is also emitted directly, but particulate matter represents the broad and prominent category typically highlighted in discussions of major primary pollutants.