The pollutants which come directly in the air from sources are called primary pollutants. Primary pollutants are sometime converted into secondary pollutants. Which of the following belongs to secondary air pollutants ?

Ozone is a toxic gas and both NO2 and O3 are strong oxidising agents and can react with the unburnt hydrocarbons in the polluted air to produce chemicals such as formaldehyde, acrolein and peroxyacetyl nitrate (PAN). 3CH4 + 2O3 → 3CH2 = O + 3H2O(Formaldehyde) CH2=CHCH=O(acrolein ),Peroxyacetyl nitrate (PAN) CH3COOONO2 . In whichNO2 and O3 are primary pollutants ,Formaldehyde, Acrolein and PAN are secondary pollutants