What are primary and secondary pollutants of the air ?

Explanation

Primary pollutants : Primary pollutants are those pollutants which enter the environment after their formation and remain as it is. For example, NO, `NO_2` `SO_2` etc. are the primary pollutants. Secondary pollutants : Secondary pollutants are those pollutants which are formed by the different chemical reactions occuring in between the primary pollutants in the atmosphere or hydrosphere. For example, oxides of nitrogen and hydrocarbons react together in the presence of sunlight to form peroxyacylnitrates (PAN) as a harmful substance.