Air Pollutants and Sources Questions and Answers

Answer: A

The major source of benzo-a-pyrene in the atmosphere is residential wood burning, in which incomplete combustion of organic matter forms polycyclic aromatic hydrocarbons.

Gasoline, coal tar and cooked meat also contain or release BaP, but according to the key the main atmospheric source is residential wood burning.

Testing each of the remaining options against the same fact shows that every one of them fails on the point the question is asking about, which confirms the keyed answer.

Answer: D

The key gives carbon monoxide as the most dominant pollutant by concentration in urban air. Vehicle exhaust produces it in large quantities by incomplete combustion, and its concentrations are in the range of milligrams per cubic metre, much higher than the microgram levels of the others.

Oxides of nitrogen and sulphur occur at microgram per cubic metre levels. Particulate matter is a major pollutant by health impact and is measured in micrograms per cubic metre as well. The answer is option D.

Answer: A

Chlorine gas, Cl2, is a primary pollutant.

A primary pollutant is emitted directly from a source, and chlorine escapes directly from chemical plants and from leaks, so it is primary.

Sulphur trioxide, SO3, forms in the air when SO2 is oxidised, and sulphates form from SO3 and moisture, so both are secondary. Nitrates form when oxides of nitrogen are oxidised and react in the atmosphere, so they are secondary too.

Answer: D

All four constituents are principal constituents of atmospheric brown clouds, so the answer is (D). These clouds are layers of air pollution over large regions, such as South Asia, made of soot (black carbon), soil dust, fly ash and aerosols of sulphates and nitrates, together with other particles.

Each of the options (A), (B) and (C) lists only some of the constituents, so none is complete.

Answer: A

The size range of atmospheric aerosols is 5 nm to 100 micrometres. This covers fine particles formed from gases, up to coarse particles such as dust and sea salt spray.

The ranges starting at 100 micrometres or 150 micrometres are too large to describe aerosols, which stay suspended in air, and 0.01 nm to 5 nm is smaller than the diameter of a molecule cluster, so it is wrong.

Answer: A

Ocimene is a hydrocarbon emitted by vegetation. Plants release terpenes such as isoprene, pinene and ocimene, and these volatile organic compounds take part in forming ozone and haze.

Xylene, acrolein and 1,3-pentadiene are emitted from industrial and combustion sources, not from vegetation, so they are wrong.

Isoprene from oak and poplar trees and terpenes from conifers react in sunlight with nitrogen oxides, so the natural emissions can add to the formation of ozone in polluted air.

Answer: A

Sulphur dioxide from a boiler stack and carbon monoxide from a vehicle exhaust are typical examples. Secondary pollutants such as ozone and much fine particulate form later in the air itself and cannot be traced to a single emission point.

Answer: B

Sunlight drives the reaction between the two precursor families, which is why urban ozone peaks in the afternoon and downwind of the city rather than in it. Controlling it means controlling its precursors rather than ozone itself.

Answer: C

The fraction penetrates deep into the alveolar region and is the size class most strongly associated with cardiopulmonary mortality. Its long atmospheric residence time also makes it a regional rather than a local problem.

Answer: D

It is the diameter of a unit density sphere with the same settling velocity, so two particles of quite different shape and density share it if they behave alike. Deposition in the lung and capture in a control device both follow that behaviour.