Which is NOT a green house gas in earth's atmosphere?
- A.Ozone
- B.Sulphur dioxide
- C.Carbon dioxide
- D.Methane
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Explanation
The correct answer is B, Sulphur dioxide. Sulphur dioxide is an air pollutant but it is not counted among the greenhouse gases.
A greenhouse gas is one that lets sunlight through but absorbs the long wave infrared radiation the earth sends back, so it warms the lower atmosphere. The main ones are water vapour, carbon dioxide, methane, nitrous oxide, ozone and the chlorofluorocarbons. Sulphur dioxide behaves in the opposite way: released by burning coal and by volcanoes, it forms fine sulphate aerosols that reflect sunlight and have a cooling effect, and in moist air it turns into sulphuric acid and causes acid rain.
Option A, ozone, is a greenhouse gas in the troposphere. Option C, carbon dioxide, is the gas most responsible for the human share of warming. Option D, methane, traps far more heat per molecule than carbon dioxide and comes largely from paddy fields, cattle and landfills.
Exam tip: sulphur dioxide causes acid rain and cools; carbon dioxide, methane, nitrous oxide and ozone warm.