Primary pollutants are directly produced from a process or from direct sources like volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone, one of the many secondary pollutants that make up photochemical smog. 

However, some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.

PRIMARY POLLUTANTS

• lanzracelis33blogspot.comSulfur Oxides
• Nitrogen oxides
• Volatile organic compounds
• Particulates
• Carbon Monoxide
• Persistent free radicals
• Chlorofluorocarbons
• Odors
• Radioactive pollutants

SECONDARY POLLUTANTS

• Particulates created from gaseous primary pollutants and compounds in photochemical smog
• Ground level ozone
• Peroxyacetyl nitrate (PAN)
• A large number of minor hazardous air pollutants.
• A variety of persistent organic pollutants, which can attach to particulates