Air pollution basics – identify primary pollutants Primary pollutants are emitted directly from sources, whereas secondary pollutants form in the atmosphere. Which pair lists two primary air pollutants?

Introduction:
Air pollutants are categorized as primary (emitted directly) or secondary (formed by chemical reactions in the atmosphere). Distinguishing the two types is essential for designing control strategies and regulatory standards. This question requires identifying a pair that contains only primary pollutants.

Given Data / Assumptions:

• Primary pollutants: SOx (e.g., SO2), NOx (NO, NO2), CO, hydrocarbons (HC), particulate matter, etc., emitted from combustion, industrial processes, and natural sources.
• Secondary pollutants: ozone (O3), peroxyacetylnitrate (PAN), secondary aerosols, formed via photochemical reactions involving NOx and VOCs.
• Ambient conditions allow typical urban photochemistry.

Concept / Approach:

Evaluate each option against the primary-versus-secondary classification. Sulphur oxide (SO2) is emitted directly from sulfur-bearing fuel combustion, smelting, and volcanism. Hydrocarbons (VOCs) are directly emitted from fuel evaporation, incomplete combustion, and industrial solvents. Ozone and PAN are hallmark secondary oxidants formed in sunlight-driven photochemical smog.

Step-by-Step Solution:

Verification / Alternative check:

Photochemical smog schematics show VOC + NOx + sunlight → O3 and PAN, confirming that these are secondary and should not appear in the correct primary pair.

Why Other Options Are Wrong:

Options A, B, and D include ozone or PAN (secondary). Option E also lists secondary species. Only Option C contains two primary species.

Common Pitfalls:

Assuming all oxidants are primary; confusing NO2 (primary + secondary) with O3 (secondary only).

Final Answer:

sulphur oxide and hydrocarbon