Which of the following is the chief component of photochemical smog?
- A.Sulphur dioxide
- B.Ozone
- C.Methane
- D.Carbon dioxide
Correct answer
Explanation
The correct answer is B, Ozone. Photochemical smog, also called Los Angeles smog, forms in warm, dry, sunny weather when oxides of nitrogen from vehicle exhaust and unburnt hydrocarbons react under ultraviolet light. Its chief oxidising components are ground-level ozone, peroxyacetyl nitrate and aldehydes, which is why it is described as oxidising smog and why it irritates the eyes and the throat. Option A is wrong because sulphur dioxide is the marker of classical or London smog, which is reducing and forms in cold, humid air. Option C is wrong because methane is a greenhouse gas from paddy fields, cattle and landfills, not a smog component. Option D is wrong because carbon dioxide drives global warming but is not a constituent of smog. Note the reversal that papers like to set: ozone in the stratosphere shields the earth from ultraviolet radiation, while the same gas at ground level is a harmful secondary pollutant.
Read the full article: Air Pollution and Air Quality: Pollutants, AQI and Laws
Practice Questions
View allWhich of the following is a secondary air pollutant?
- A.Sulphur dioxide
- B.Carbon monoxide
- C.Peroxyacetyl nitrate
- D.Particulate matter
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A secondary pollutant is never emitted from a source; it is manufactured in the atmosphere itself when primary pollutants react with one another or with sunlight.
Read the full explanation →Carbon monoxide is dangerous to human beings mainly because it:
- A.Combines with haemoglobin to form carboxyhaemoglobin
- B.Dissolves in water to form a strong acid
- C.Destroys the ozone layer of the stratosphere
- D.Settles in the alveoli as fine dust
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Carbon monoxide binds to the haemoglobin of the blood roughly two hundred times more readily than oxygen does, and the carboxyhaemoglobin so formed cannot carry oxygen.
Read the full explanation →Along with the oxides of nitrogen, which gas is chiefly responsible for acid rain?
- A.Carbon monoxide
- B.Methane
- C.Sulphur dioxide
- D.Argon
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Sulphur dioxide, released when coal and oil containing sulphur are burnt, is oxidised in the atmosphere to sulphur trioxide, which dissolves in water droplets to give sulphuric acid.
Read the full explanation →The damage to the marble of the Taj Mahal, popularly called 'marble cancer', is caused chiefly by:
- A.Carbon dioxide
- B.Sulphur dioxide
- C.Chlorofluorocarbons
- D.Ground-level ozone
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Sulphur dioxide from industry and traffic around Agra is oxidised in the air and comes down as sulphuric acid, which attacks the calcium carbonate of marble.
Read the full explanation →PM2.5, the pollutant reported in air quality bulletins, refers to particles whose diameter is:
- A.2.5 millimetres or less
- B.2.5 nanometres or less
- C.2.5 micrometres or less
- D.2.5 centimetres or less
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Particulate matter is graded by the diameter of the particles measured in micrometres, so PM10 means particles of ten micrometres or less and PM2.5 means particles of 2.5 micrometres or less, which is about thirty times finer than a human hair.
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