Which substance is not categorized as a secondary air pollutant?
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Answer: C. Sulphur dioxide
Explanation
Sulfur dioxide is a primary air pollutant emitted directly from combustion sources rather than a secondary pollutant. Secondary air pollutants form in the atmosphere through chemical reactions involving primary pollutants and sunlight. Sulfur dioxide acts as a precursor that eventually oxidizes and forms secondary particulate sulfates in the air. Primary pollutants are injected directly into the atmosphere from smokestacks, vehicles, and natural eruptions. Secondary pollutants include ground-level ozone, photochemical smog, and various organic aerosol compounds. Fossil fuel combustion in power plants releases large amounts of primary sulfur dioxide gas.
Air pollution control strategies must distinguish between primary and secondary pollutants to target emission sources effectively. Controlling primary sulfur dioxide emissions helps reduce regional acid deposition and secondary sulfate haze. Environmental monitoring networks track both primary gases and secondary photochemical pollutant concentrations. Ozone is a classic secondary pollutant created via photochemical reactions involving nitrogen oxides and hydrocarbons. Photochemical smog is a complex secondary pollutant mixture formed under intense sunlight in urban atmospheres. Grouping all three options together is incorrect because sulfur dioxide belongs strictly to the primary pollutant category.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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