Which emitted compounds most often occur as precursors to secondary pollutants?

Which emitted compounds most often occur as precursors to secondary pollutants?

• A. Nitric oxide and elemental sulfur
• B. Nitric oxide and sulfur dioxide
• C. Nitrogen dioxide and sulfur dioxide
• D. Nitrogen dioxide and sulfur trioxide

Answer: (B)

Secondary pollutants come from reactions that occur after primary pollutants are released into the air. The most important emitted precursors are nitrogen oxides and sulfur dioxide. Nitrogen oxides, released from vehicles and power plants, participate in photochemical reactions that lead to ozone and nitrate-containing aerosols. Sulfur dioxide, from burning fossil fuels, oxidizes to form sulfuric acid and sulfate particles, which are key components of fine particulate matter and acid rain. Because these two gases are the most widely emitted and drive the major pathways to secondary pollutants, nitric oxide and sulfur dioxide together best represent the common precursors. Elemental sulfur is not typically emitted in large amounts, and sulfur trioxide or nitrogen dioxide alone don’t capture the predominant precursors as effectively.

Secondary pollutants come from reactions that occur after primary pollutants are released into the air. The most important emitted precursors are nitrogen oxides and sulfur dioxide. Nitrogen oxides, released from vehicles and power plants, participate in photochemical reactions that lead to ozone and nitrate-containing aerosols. Sulfur dioxide, from burning fossil fuels, oxidizes to form sulfuric acid and sulfate particles, which are key components of fine particulate matter and acid rain. Because these two gases are the most widely emitted and drive the major pathways to secondary pollutants, nitric oxide and sulfur dioxide together best represent the common precursors. Elemental sulfur is not typically emitted in large amounts, and sulfur trioxide or nitrogen dioxide alone don’t capture the predominant precursors as effectively.