Previous Year Question
Consider the following which can be found in the ambient atmosphere:
Soot
Sulphur hexafluoride
Water vapour
Which of the above contribute to the warming up of the atmosphere?
1 and 2 only
3 only
2 and 3 only
All of these
Correct Answer: D
Detailed Solution
Soot, sulphur hexafluoride and water vapour—all three can contribute to atmospheric warming through different processes.
Soot: Light-absorbing carbon particles present in soot are generally known as black carbon.
Black carbon is produced through the incomplete combustion of fossil fuels, biofuels and biomass.
It absorbs incoming solar radiation and heats the surrounding air, thereby producing a direct warming effect.
When deposited on glaciers and snow, black carbon reduces the reflectivity or albedo of the surface.
A reduction in albedo causes the ice to absorb more solar energy and may accelerate its melting.
Black carbon remains in the atmosphere for a shorter period than carbon dioxide and is therefore considered a short-lived climate pollutant.
Sulphur hexafluoride (SF₆): It is an anthropogenic, colourless, odourless and extremely persistent greenhouse gas.
Because of its excellent electrical-insulation properties, it is used in high-voltage electrical equipment, switchgear and circuit breakers.
SF₆ absorbs outgoing infrared radiation from the Earth extremely effectively.
Its global warming potential is several thousand times greater than that of carbon dioxide, and it can remain in the atmosphere for thousands of years.
Although its atmospheric concentration is low, each unit of emission produces a very large long-term warming effect.
Water vapour: It is the most abundant naturally occurring greenhouse gas in the atmosphere.
Water vapour absorbs outgoing longwave infrared radiation from the Earth’s surface and radiates a portion of it back towards the surface.
This process helps maintain the temperature of the lower atmosphere and the Earth’s surface.
Water vapour is mainly regarded as a climate feedback—as temperature increases, evaporation and the atmosphere’s capacity to hold water vapour increase.
Additional water vapour absorbs more infrared radiation and can amplify the initial warming; this is called positive water-vapour feedback.
Therefore, soot, sulphur hexafluoride and water vapour—all three contribute to atmospheric warming.