Peroxyacetyl nitrate (PAN)

PAN – photochemical smog mainly consist of ozone, peroxyacetyl nitrate (PAN) and nitrogen oxides (NOx).

Photochemical smog

It is formed by the reaction of hydrocarbons and nitrogen oxides in the atmosphere in presence of sunlight. It is mainly formed in traffic congested areas in metro cities where warm conditions and intense solar radiation are present.

Greenhouse effect

Green house gases like CO₂, CH₄, N₂O of atmosphere form a blanket over the earth that controls the escape of heat from the surface of earth to outer space so as to keep it warm and cosy. This phenomenon is called greenhouse effect. The mean annual temperature of earth is about 15^oC. if there would have no greenhouse gases in the earth, mean temperature would go sharply down to about – 20^oC.

Brown Air

Nitrogen oxides cause reddish brown haze in traffic congested city air, called ‘brown air’.

Grey Air

In areas of lesser solar radiation, smog formation is incomplete and the air is referred to as ‘grey air’.