Photochemical smog is a mixture of pollutants which includes particulates, nitrogen oxides, ozone, aldehydes, peroxyethanoyl nitrate (PAN), unreacted hydrocarbons, etc. The smog often has a brown haze due to the presence of nitrogen dioxide. It causes painful eyes.

The Cause

The condition needed for the formation of the smog are present in modern cities. They included sunlight, hydrocarbons, nitrogen oxides and particulates which act as catalyst.

These are the equations in the formation of photochemical smog.

Case Study

On 9 December 1952, foggy conditions developed over London. Being very cold, most houses kept fires burning, with coal as the major fuel. The smoke from these fires mixed with the fog and was unable to disperse, resulting in a smog which persisted for 4 days. The pH of air during the Great London Smog was as low as 1.6. During this period some 4000 more people died than would expected at this time of the year. Most of these additional deaths were due to respiratory disorders.

New York City, before and after a photochemical smog.

Effects

1. It can cause headaches, eye, nose and throat irritations. It may cause the lung function impaired, coughing and wheezing.
2. It can cause rubbers and fabrics to deteriorate.
3. It can damage plants, leading to the loss of crops.

Related Topics

Nitrogen oxides
Ozone
Hydrocarbons
Particulates

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