Ozone is a strong oxidising agent like NO2. In troposphere both O3 and NO2 react with the unburnt hydrocarbons to produce the chemical components of photochemical smog, like formaldehyde (HCHO), acrolein (CH2=CH−CHO) and PAN or peroxyacetyl nitrate (CH3−
C
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O
−O−O−NO2) Hence, in troposphere, the presence of ozone generates photochemical smog.