SMOG

The poisonous mixture of smoke, fog, air and other chemicals is called smog. Smog is a major pollution problem in big cities. Smog is usually formed during winter. There are two general types of smog:

1. Photochemical Smog (Los Angels Smog)2. Chemical Smog (London Smog)

Photochemical Smog (Los Angels Smog)The smog which is generally initiated by the UV radiation from the sun, is known as photochemical smog. The other gradients for the formation of this type of smog are (NO + NO2), unburnt hydrocarbons and SO2. When oxides of nitrogen and hydrocarbons, produced by the combustion of fuels in automobiles and in industries, absorb UV rays, the process of smog formation is initiated. NO2 splits up into reactive species and starts a number of chain reactions in which the hydrocarbons are involved. This results in the formation of many secondary pollutants.

N2 (g) + O2 (g) 2NO (g)

2NO (g) + O2 (g) 2NO2 (g)

NO2 (g) NO (g) + [O]

O2 (g) + [O] O3 (g)

Hydrocarbons + O3, [O], NO2 Peroxides, Peroxyacetyl nitrate (PAN), formaldehyde, ozone aldehyde, acrolein etc. (Oxidized hydrocarbons)

In presence of humidity, oxidized hydrocarbons and ozone cause photochemical smog, which is characterized by the formation of aerosols that reduce visibility, generation of brown hazy fumes, which causes irritation of eyes and lungs and also causes extensive damage to vegetation and rubber goods.This type of smog was observed in some parts of Los Angels and that is why it is sometimes referred to as Los Angels Smog.

Chemical Smog (London Smog)This type of smog is thought to be caused by SO2. It is formed by combination of smoke, dust, fog and SO2. Chemical smog is usually formed around some industrial and power plants. It is generally bad in the early morning hours and becomes worse after sunrise, due to sunlight-induced oxidation of SO2 to SO3, followed by reaction with humidity. Sulphuric Acid is formed in this type of smog, which is very harmful to people suffering from bronchial diseases such as asthma or emphysema.In the year 1962, more than 700 persons were killed by chemical smog in London that’s why chemical smog is also referred as to as London Smog.

In IC engines esenginesOr furnaces

UV light