Smog is an example of the formation of what kind of pollutant, which occurs when primary pollutants undergo chemical reactions after they are released?
primary pollutant
combined pollutant
tertiary pollutant
secondary pollutant
Primary pollutants enter the air directly. They include carbon, nitrogen, and sulfur oxides. Toxic heavy metals, VOCs, and particulates are also primary pollutants. Secondary pollutants form when primary pollutants undergo chemical reactions after they are released. Many occur as part of photochemical smog. The main component of smog is ozone.