Describe the two main types of urban smog and their primary pollutants.

Describe the two main types of urban smog and their primary pollutants.

• A. Photochemical smog is caused by NOx and VOCs producing ozone.
• B. London-type smog from burning coal containing SO2 and particulates.
• C. London-type smog from burning coal with SO2 and particulates; photochemical smog from NOx and VOCs producing ozone under sunlight.
• D. Smog is solely caused by motor vehicle exhaust, with no other pollutants.

Answer: (C)

Urban smog comes in two well-established forms, defined by their sources and the chemistry that creates them. The sulfurous, London-type smog arises when fossil fuels—especially coal—are burned in cool, damp conditions. Sulfur dioxide and fine particulates dominate this mix, and the polluted fog becomes heavy and gray as these pollutants interact with water droplets. The photochemical, Los Angeles-type smog forms in sunny, warm conditions when emissions from vehicles and other fuels release nitrogen oxides and volatile organic compounds; sunlight drives reactions between NOx and VOCs to produce ozone and other oxidants, creating a bright, hazy, often brownish atmosphere rich in photochemical pollutants. So, the best description captures both forms: London-type smog from coal combustion with sulfur dioxide and particulates, and photochemical smog from NOx and VOCs producing ozone under sunlight. This contrast highlights how different pollutants and atmospheric conditions lead to distinct smog types. The other options focus on only one form or misattribute the primary pollutants, which doesn’t reflect the two-category framework that correctly explains urban smog.

Urban smog comes in two well-established forms, defined by their sources and the chemistry that creates them. The sulfurous, London-type smog arises when fossil fuels—especially coal—are burned in cool, damp conditions. Sulfur dioxide and fine particulates dominate this mix, and the polluted fog becomes heavy and gray as these pollutants interact with water droplets. The photochemical, Los Angeles-type smog forms in sunny, warm conditions when emissions from vehicles and other fuels release nitrogen oxides and volatile organic compounds; sunlight drives reactions between NOx and VOCs to produce ozone and other oxidants, creating a bright, hazy, often brownish atmosphere rich in photochemical pollutants.

So, the best description captures both forms: London-type smog from coal combustion with sulfur dioxide and particulates, and photochemical smog from NOx and VOCs producing ozone under sunlight. This contrast highlights how different pollutants and atmospheric conditions lead to distinct smog types. The other options focus on only one form or misattribute the primary pollutants, which doesn’t reflect the two-category framework that correctly explains urban smog.