Which of the following is a secondary pollutant?
2023
Which of the following is a secondary pollutant?
Answer: D. More than one of the above — ConceptA primary pollutant is emitted directly from a source. A secondary pollutant is produced in the atmosphere when primary pollutants react under…
- A.
PAN
- B.
SO2
- C.
Ozone
- D.
More than one of the above
- E.
None of the above
Show answer & explanation
Correct answer: D
Concept
A primary pollutant is emitted directly from a source.
A secondary pollutant is produced in the atmosphere when primary pollutants react under conditions such as sunlight; photochemical oxidants are standard examples.
Application
PAN forms during photochemical reactions involving nitrogen oxides and products of volatile-organic-compound oxidation.
Ground-level ozone forms photochemically from nitrogen oxides and volatile organic compounds in sunlight.
Sulfur dioxide is commonly emitted directly when sulfur-containing fuels burn, so it is classified as a primary pollutant in this context.
Contrast
PAN: a photochemical-smog product formed in air.
SO2: chiefly a direct combustion emission.
Ozone: a photochemical oxidant formed in air.
Cross-check
Both PAN and ozone satisfy the atmospheric-formation test, whereas SO2 fits the direct-emission test. Therefore, more than one of the listed pollutants is secondary.