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Photochemical smog forms through the interaction of pollutant gases, water vapor, and particulate matter like dust and carbon. The gases typically present in photochemical smog include NO₂, PAN, and O₃.

1. A primary pollutant remains in the environment in the same form as it was emitted, such as carbon monoxide (CO). A secondary pollutant, like PAN (Peroxyacetyl nitrate), is produced through reactions involving other pollutants.
2. Carbon dioxide acts as a greenhouse gas, trapping heat from solar radiation and contributing to the warming of the Earth's atmosphere.
3. Inhaling carbon monoxide causes it to bind with hemoglobin in the blood to form carboxyhemoglobin, which occurs 210 times faster than the binding of oxygen to form oxyhemoglobin, thereby hindering respiration.
4. Hyperbaric oxygen therapy (HBO) is used to treat elevated carboxyhemoglobin levels by exposing patients to pure oxygen under high pressure, reducing the half-life of carboxyhemoglobin from about 90 minutes under normal oxygen conditions to roughly 30 minutes during HBO.

Correct answer: A primary pollutant remains in the environment in the same form as it was emitted, such as carbon monoxide (CO). A secondary pollutant, like PAN (Peroxyacetyl nitrate), is produced through reactions involving other pollutants.

Solution

Option A correctly distinguishes between primary and secondary pollutants, with examples like CO and PAN, which are relevant to photochemical smog formation.

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