SMOG

Subject : Environment

Context : SC asks Centre to ensure Delhi – NCR is smog free.

Concept :

Smog = smoke + fog (smoky fog) caused by the burning of large amounts of coal, vehicular emission and industrial fumes (Primary pollutants).
Smog contains soot particulates like smoke, sulphur dioxide, nitrogen dioxide and other components.
At least two distinct types of smog are recognized: sulfurous smog and photochemical smog.

Sulfurous smog

Sulfurous smog results from a high concentration of Sulphur Oxides in the air and is caused by the use of sulfur-bearing fossil fuels, particularly coal.
This type of smog is aggravated by dampness and a high concentration of suspended particulate matter in the air.

Photochemical smog

Photochemical smog occurs most prominently in urban areas that have large numbers of automobiles (Nitrogen oxides are the primary emissions).
Photochemical (summer smog) forms when pollutants such as nitrogen oxides (primary pollutant) and organic compounds (primary pollutants) react together in the presence of Sunlight. A gas called Ozone (Secondary pollutant) is formed.
Nitrogen Dioxide + Sunlight + Hydrocarbons = Ozone (Ozone in stratosphere it is beneficial, but near the earth’s surface it results in global warming as it is a greenhouse gas)
The resulting smog causes a light brownish coloration of the atmosphere, reduced visibility, plant damage, irritation of the eyes, and respiratory distress.

Effects of Smog

The atmospheric pollution levels of Los Angeles, Beijing, Delhi, Mexico City and other cities are increased by temperature inversion that traps pollution close to the ground.
It is usually highly toxic to humans and can cause severe sickness, shortened life or death.
Smog is a combination of airborne particulate matter, like soot, and invisible toxic gases including ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), which are carcinogens (cancer causing agents).
Temperature inversions are accentuated and precipitation is reduced.
Smog related Haze lowers visibility.