Air Pollution and Its Control Questions and Answers

Answer: A

SPM stands for Suspended Particulate Matter.

SPM is the general term for the fine solid particles and liquid droplets suspended in the air, such as dust, smoke, soot and fly ash. It is a key measure of air pollution, and its finer fractions, PM10 and PM2.5, can enter deep into the lungs and cause respiratory and heart disease.

'Suspended Particle Matter' is a near-miss wording, not the standard term. Sulphur monoxide is an unstable gas, unrelated to the abbreviation; the common sulphur pollutant is sulphur dioxide. Since one option is correct, 'None of the above' is wrong.

Answer: C

The secondary pollutant is PAN (peroxyacetyl nitrate).

A secondary pollutant is not emitted directly but forms in the atmosphere when primary pollutants react. PAN is produced when hydrocarbons and nitrogen oxides from vehicle exhaust react in sunlight, and it is a key component of photochemical smog, irritating the eyes and damaging plants.

Carbon monoxide and carbon dioxide are primary pollutants emitted directly by combustion. Aerosols are mostly emitted directly too (dust, smoke), so they are not the clear example of a secondary pollutant the question seeks.

Answer: B

The key's answer is oxides of nitrogen.

Nitrogen oxides, from supersonic aircraft exhaust and from nitrous oxide released by fertilisers, react with ozone in the stratosphere and break it down, which is why they are named among the causes of ozone depletion. The chlorine from chlorofluorocarbons is the other main culprit.

Oxides of carbon (carbon dioxide and monoxide) and of phosphorus do not destroy stratospheric ozone in this way.

Answer: B

Ozone layer thickness is measured in Dobson units.

One Dobson unit is the amount of ozone that would form a layer 0.01 mm thick if all the ozone in a column of the atmosphere were compressed to standard temperature and pressure. A typical total is about 300 DU; an 'ozone hole' is usually defined as values below 220 DU.

Decibels measure sound intensity. PPB and PPM are concentration units used for gases near the ground, not for the total column of ozone overhead.

Answer: C

Both statements are correct, so the answer is Both 1 and 2.

Styrene, the monomer from which polystyrene plastics and resins are made, is a flammable liquid at room temperature and is stored as a liquid in tanks, ideally below about 20 degrees Celsius. The May 2020 disaster at LG Polymers in Visakhapatnam happened when the stored liquid heated up and polymerised in an uncontrolled way, releasing vapour (1).

Short exposure irritates the eyes and mucous membranes and causes gastrointestinal and breathing problems, while long exposure affects the central nervous system and high doses can kill (2). So 'Only 1', 'Only 2' and 'Neither' each reject a correct statement.

Answer: A

A three-way converter reduces hydrocarbons, carbon monoxide and nitric oxide, so the answer is Only 1, 2, and 3.

The converter is called three-way because it handles three pollutants at once. Platinum and palladium catalysts oxidise unburnt hydrocarbons and carbon monoxide to carbon dioxide and water, and rhodium reduces oxides of nitrogen such as nitric oxide to nitrogen.

It does not remove sulphur dioxide; sulphur in fuel actually poisons the catalyst, which is why low-sulphur fuel is needed. So every option including 4 is wrong.

Answer: C

The ozone layer absorbs ultraviolet radiations.

Ozone (O₃) in the stratosphere, about 15 to 35 km up, absorbs most of the Sun's harmful ultraviolet radiation, especially UV-B and UV-C, which would otherwise damage DNA and cause skin cancer and cataracts. Thinning of the layer by chlorofluorocarbons is why the Montreal Protocol was adopted.

Visible light and radio waves pass through the atmosphere largely unabsorbed, and infrared radiation is absorbed mainly by water vapour and carbon dioxide, not by the ozone layer.

Answer: D

Dust particles from the burning of wastes can be stopped from escaping into the air by an electrostatic precipitator, which charges the particles and collects them on plates, option D.

An air conditioner, a bioreactor and a ventilator do not remove particulates from flue gas.

An electrostatic precipitator gives the dust particles an electric charge as the flue gas passes between plates, and then collects them on plates of opposite charge, removing over 99 per cent of the dust from the exhaust of power plants and incinerators. Air conditioners and ventilators only move air, and a bioreactor is used for biological treatment.

Answer: A

The commission's key takes both [A] and [R] as correct with [R] explaining [A], option A. The statements describe a comparative study of air-pollution control, in which the Chinese state, working through its institutions, handled the problem differently from India, where mass politics played the larger role.

Options that call either statement false or deny the explanation contradict the key. This is a recent-affairs item that could not be independently verified here, so the explanation rests on the key.

Answer: A

The keyed answer is Global warming.

Of the four options, global warming is the only one with any link to the ozone layer. The chemicals that destroy ozone, such as CFCs and halons, are also powerful greenhouse gases, and the loss of ozone is bound up with changes in the climate. That is why a question that asks what ozone depletion is responsible for is keyed to global warming.

The more direct effect of a thinner ozone layer is more ultraviolet radiation reaching the ground, which causes skin cancer and cataract and harms crops and plankton, so the keyed link is the indirect one. De-forestation, landslides and earthquakes have nothing to do with the ozone layer, so the other three options are wrong.