Question

Primary constituents of photochemical smog are
a. Sulphur dioxide and carbon monoxide
b. Carbon dioxide and nitrous oxide
c. Nitrous oxide and hydrocarbons
d. Hydrocarbons and CFCs

Answer 1

Hint: Smog is opaque or dark fog comprises dust, water vapour and gases. Smog is of two types: Photochemical smog and London smog or classical smog. Smog is a type of air pollution which reduces visibility.

Complete answer:
• Photochemical smog: This type of smog is present in congested cities where warm conditions and intense solar radiation are present. It comprises ozone, PAN (peroxyacetyl nitrate) and nitrogen oxides. It is also known as brown air and grey air. Ozone corrodes the heritage building surface and damages the marble. PAN inhibits ETS and damages chloroplasts.

• London smog or classical smog: It occurs at low temperature and contains sulphur dioxide. It is also known as dark brown hair. Secondary pollutants have no role in the London smog.

Today, most of the smog we see is photochemical smog.
Primary constituents of photochemical smog are nitrous oxide and hydrocarbons. Photochemical smog comprises both primary and secondary air pollutants.

• Primary air pollutants: Air pollutants which are coming directly from the pollution sources (vehicles, factories, smelters and thermal power plants). Carbon monoxide, sulphur dioxide, oxides of nitrogen and hydrocarbons are the examples of primary air pollutants.

• Secondary air pollutants: These pollutants obtained by the reaction between two or more primary air pollutants and the resulting product are known as secondary air pollutants. Ozone and PAN are examples of secondary air pollutants.

Pollutant	Source	Effects
Oxides of nitrogen	Combustion of fossil fuels at high temperature.	Heart and lung problems.
Hydrocarbons	Incomplete combustion, newly manufactured carpet.	Cancer

Hence, the correct answer is option (c).

Note: To control the air pollution, the government of india comes up with the Air (prevention and control of pollution) Act, 1981. This act deals with the preservation of air quality and the control of air pollution with the concern for the detrimental effects of air pollutants on plants and animals.