what primary pollutants are needed for a formation
Sulfur dioxide and nitric oxide (NO) are the primary air pollutants, and ozone is a secondary pollutant (though there are negligible direct emissions of the gas itself). Nitrogen dioxide (NO2) is both a primary and secondary air pollutant. Other important gaseous pollutants are: ammonia, carbon monoxide, volatile organic compounds (VOCs) and persistent organic pollutants (POPs) which we discuss below.