Question

How hydroxyl radicals produced from the primary smog forming reactions & the secondary smog forming reactions ? (type it here and explain it in simple language)

how the pollutants dispersed into the atmosphere in the normal conditions ? and why pollutants get trapped in the atmosphere  in temperature inversion ? (type it here and explain it in simple language)

why N2 does not react with O2 in the atmosphere?

Answer 1

Air pollutants such as nitric oxide, nitrogen dioxide are produced from vehicle, burningof fossil fuels and natural calamities. These create highly reactive radicals. Primary smog is produced by direct involvement of pollutants where as secondary smog is produced by the product of primary smog.

The reaction of formation of HO• is as follows:

Primary smog

R• + O2+ M ---> RO2• + M

RO2• + NO ---> NO2 + RO•

HO2• + NO ---> NO2 + HO•

Secondary smog

NO2 and NO further react with O3 in a series of reactions

NO2 + hv ---> O + NO

O + O2 + M ---> O3 + M(heat)

O3 + NO ---> NO2 + O2

HO2• + R• --> RO• + •OH

Dispersion of pollutants takes place in air can be simulated by mathematical model. Though simply it can be said that, crosswind dispersion, vertical dispersion takes place. It related to emission rate and height of emission of source point, degree of turbulence in air etc. Convection process also associated with this. So, several factors are related to this process.

Pollutants are trapped due to invertion temperature gradients which is produced by volcanic eruption or ash coming from industry. Invertion temperature is increasing temperature with increasing altitude. This acts like a sheath or blanket which inhibits the natural vertical airflow and increase temperature. This process traps pollutants to produce smog.

N2 doesn't react at ambient temperature because of its NN triple bond which is very difficult to break and activate to react. So, due to very high bond energy of NN triple bond, it is inert and doesn't react.