Which of the following best describes the difference between a primary and a secondary pollutant?

• A. A primary pollutant is always a gas, while a secondary pollutant is always a solid.
• B. A primary pollutant is emitted directly into the atmosphere, while a secondary pollutant forms in the atmosphere through chemical reactions.
• C. A primary pollutant is produced by natural sources, while a secondary pollutant is produced by human activities.
• D. A primary pollutant is less harmful than a secondary pollutant.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the definitions of primary and secondary pollutants. A primary pollutant is a substance that is emitted directly into the atmosphere from a source, such as carbon monoxide from vehicle exhaust.
2. Step 2: Recognize that a secondary pollutant is not emitted directly but forms in the atmosphere through chemical reactions involving primary pollutants and other atmospheric components, such as ozone formed from nitrogen oxides and volatile organic compounds under sunlight.
3. Step 3: Evaluate the given options by comparing them to these definitions. For example, the statement that a primary pollutant is always a gas and a secondary pollutant is always a solid is incorrect because pollutants can exist in various phases.
4. Step 4: Identify that the correct description is the one stating that a primary pollutant is emitted directly into the atmosphere, while a secondary pollutant forms in the atmosphere through chemical reactions.
5. Step 5: Confirm that other options, such as the source being natural versus human activities or the relative harm of pollutants, do not accurately capture the fundamental difference between primary and secondary pollutants.