Which among the following is the secondary pollutant?

Q. Which among the following is the secondary pollutant?

1. Smog
2. Carbon dioxide
3. Carbon mono-oxide
4. Fly ash

Answer: Smog

Secondary pollutant form when primary pollutants emitted directly from a combustion process react in the atmosphere. Primary pollutants include ammonia, sulfur dioxide, nitrogen dioxide and carbon monoxide. Secondary pollutants include ground-level ozone, acid rain and nutrient enrichment compounds.

Smog is a type of air pollutant. The word "smog" was coined in the early 20th century as a portmanteau of the words smoke and fog to refer to smoky fog, its opacity, and odor.

Modern smog, as found for example in Los Angeles, is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog. In certain other cities, such as Delhi, smog severity is often aggravated by stubble burning in neighboring agricultural areas. The atmospheric pollution levels of Los Angeles, Beijing, Delhi, Lahore, Mexico City, Tehran and other cities are increased by inversion that traps pollution close to the ground. It is usually very highly toxic to humans and can cause severe sickness, shortened life or death.