Question

What is smog? How is classical smog different from photochemical smog?

Answer 1

- .Hint: The word smog is derived from two words ‘smoke’ and ‘fog’. Photochemical relates to the chemical action caused by light.


Complete step-by-step solution -

Smog is caused by various air pollutants and it is a type of intense air pollution. It is also known as smoky fog. Let us understand more about smog.
Smog is visible air pollution and it is mainly composed of oxides of sulphur and nitrogen, smoke, ozone and other particulates.
Man-made smog can come from various sources such as industrial emissions, automobile emissions, forest fires, coal combustion, etc.
We can categorize smog into two different categories based on the season – Winter smog and Summer smog.
The fog that occurs in the summer season forms due to the photochemical formation of ozone. In the summer season, there is a lot of sunlight and high temperatures. As a result, the photochemical smog is dominant.
During the winter season, the temperatures are very low due to which the consumption of coal and other fossil fuels increases for heating purposes in households. The emissions from these excessive combustions of fossil fuel results in winter smog.
Classical smog is the smog that is dominant during the winter season while photochemical smog is dominant during the summer season.
Classical fog contains oxides of sulphur and nitrogen and it has reducing properties. Reducing properties refers to the property of an element or compound to donate electrons. It undergoes oxidation itself by losing electrons.
Photochemical smog is mainly derived from vehicle emission. The pollutants released from the vehicles react with sunlight and form secondary pollutants such as ozone. The secondary pollutants along with the primary pollutants form the photochemical smog.
A primary pollutant is emitted directly from the source while a secondary pollutant is formed in the atmosphere when the primary pollutants react in the atmosphere.

Note: Don’t confuse between smog and smoke. Smoke is mainly formed due to the burning of substances. They are visible vapours or gases and fine particles that are released when something is burnt in the presence of air.