Smog and Photochemical Smog

Smog is nothing but a combination of smoke and fog. Smog occurs due to the factors like geography, sunlight, industrial activity, vehicular emissions, calmness of winds, burning of coal etc. Smog usually occurs at a place which is far away from the actual source of pollution. At least two distinct types of smog are recognized:

1. Sulfurous smog (or ‘London-type’ smog)
2. Photochemical smog (‘Los Angeles-type’ smog)

Photochemical smog is the result of the action of ultraviolet radiation from sun on atmosphere polluted with pollutants such as nitrogen oxides and hydrocarbons. Photochemical smog can take place only in the presence of sunlight. Photochemical smog is a widespread problem in industrial cities all over the world. In India, northern India, especially Delhi suffers from photochemical fog especially at the time of stubble burning in neighbouring states like Punjab and Haryana.

Byproducts of Smog

There are two byproducts of smog:

1. Particulate matter:

Particulate matter is the sum of all solid and liquid particles suspended in air many of which are hazardous.  It is of two types: PM 2.5 and PM 10

2. Ground-level ozone:

O3 is a colorless, odorless gas at ambient concentrations and is a major component of smog. Ground-level ozone is not emitted directly into the atmosphere.It results from photochemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.