Dinitrogen and dioxygen are the main constituents of air. These gases do not react with each other at a normal temperature. At high altitudes when lightning strikes, they combine to form oxides of nitrogen.
N2(g)+O2(g)→2NO(g)
NO reacts instantly with oxygen to give NO2
2NO(g)+O2(g)→2NO2(g)
Rate of production of NO2 is faster when nitric oxide reacts with ozone in the stratosphere
The irritant red haze in the traffic and congested places is due to oxides of nitrogen. Higher concentrations of NO2 damage the leaves of plants and retard the rate of photosynthesis. It is toxic to living tissues also