Which of the following is NOT one of the primary air pollutants?

Ozone is classified as a secondary pollutant rather than a primary pollutant. Primary air pollutants are those emissions that are directly released into the atmosphere and can have harmful effects on health and the environment immediately upon release. Examples include carbon monoxide, nitrogen oxides, and particulate matter, which are directly emitted from sources like vehicles, industrial processes, and burning fossil fuels.

Ozone, on the other hand, forms in the atmosphere through a chemical reaction between primary pollutants, such as nitrogen oxides and volatile organic compounds, in the presence of sunlight. This formation process distinguishes it as a secondary pollutant, making it different from the others listed. This concept is important in understanding air pollution dynamics and the different categories of pollutants that affect air quality and public health.