What are the names and chemical formulas for three of the most studied pollutants (primary or secondary) ?

1. CH4 (hydrocarbons) - - primary pollutant

2. NO2 (nitrogen dioxide) - - primary pollutant

3. O3 (Ozone) - - secondary pollutant

A primary pollutant is an air pollutant emitted directly from a source while a secondary pollutant is not directly emitted but forms when other pollutants (primary pollutants) react in the atmosphere.