Which statement about primary pollutants is true?

Which statement about primary pollutants is true?

• A. Primary pollutants emitted directly into the air
• B. Primary pollutants formed from secondary reactions
• C. Primary pollutants removed by precipitation
• D. Primary pollutants are only natural substances

Answer: (A)

Primary pollutants are pollutants that are released directly into the atmosphere from a source. This means they exist in the air in the form they are when emitted, before any atmospheric reactions occur. Examples include carbon monoxide from vehicle exhaust, sulfur dioxide and nitrogen oxides from burning fossil fuels, and particulates from combustion. In contrast, secondary pollutants form in the air through reactions of primary pollutants with sunlight, water, or other chemicals—like ground-level ozone or sulfuric acid formed from SO2. Precipitation can remove pollutants from the air, but that describes removal, not how the pollutant originally enters the atmosphere. And primary pollutants include both natural and man-made substances, not only natural ones. So the statement that primary pollutants are emitted directly into the air is the best description.

Primary pollutants are pollutants that are released directly into the atmosphere from a source. This means they exist in the air in the form they are when emitted, before any atmospheric reactions occur. Examples include carbon monoxide from vehicle exhaust, sulfur dioxide and nitrogen oxides from burning fossil fuels, and particulates from combustion.

In contrast, secondary pollutants form in the air through reactions of primary pollutants with sunlight, water, or other chemicals—like ground-level ozone or sulfuric acid formed from SO2. Precipitation can remove pollutants from the air, but that describes removal, not how the pollutant originally enters the atmosphere. And primary pollutants include both natural and man-made substances, not only natural ones.

So the statement that primary pollutants are emitted directly into the air is the best description.