Question

Which is always present in photochemical smog?
A. $C{O_2}$
B. $S{O_2}$
C. $C{H_4}$
D. ${O_3}$

Answer 1

The photochemical smog is most common in summer because vehicles directly produce smoke, the smoke contains harmful chemicals that permeate the city, and many people may suffer adverse health effects.

Complete answer: Photochemical smog is a smog produced when ultraviolet rays from the sun react with nitrogen oxides in the atmosphere. Nitrogen oxides split into nitric oxide and nascent oxygen. Nascent oxygen forms ozone. Cities that encounter smog every day include Los Angeles, Sydney, Mexico City and Beijing. Nitric oxide and nitrogen dioxide are emitted from the combustion of fossil fuels, along with emissions from volcanoes and forest fires. When it is exposed to ultraviolet radiation, Nitrogen dioxide goes through a complex series of reactions with hydrocarbons to produce the components of photochemical smog which is a mixture of ozone, nitric acid and aldehydes.
Effects: Photochemical smog has many adverse effects. When combined with hydrocarbons, the chemicals contained in them can form molecules that cause eye irritation. Free radicals in the air interfere with the nitrogen cycle by preventing the destruction of ground ozone. Other effects include reduced visibility and respiratory diseases. It also produces ground-level ozone, which has various effects on the human body.
Thus, the option (D) is correct.

Note: Many techniques are used to control or reduce the formation of photochemical smog. If we control the main precursors of photochemical smog, such as $N{O_2}$ and hydrocarbons, and secondary chemicals, such as ozone and PAN, the photochemical smog will automatically be reduced.