Effects of Air Pollution Questions and Answers

Answer: A

Its affinity for haemoglobin is more than two hundred times that of oxygen, so even small concentrations occupy a large share of the binding sites. The blood carries less oxygen while appearing outwardly normal, which is what makes the gas so insidious.

Answer: B

Correct answer: Haemoglobin bound to carbon monoxide

Carboxyhaemoglobin saturation is the percentage of the blood's haemoglobin that is bound to carbon monoxide rather than to oxygen. It is the standard measure of internal dose, because it reflects what has actually reached the bloodstream rather than what was present in the air.

Carbon monoxide binds haemoglobin some 200 to 250 times more strongly than oxygen does, so even a few parts per million in air produce a measurable saturation. The result is reduced oxygen carriage, felt first as headache and impaired judgement, and dangerous at higher levels.

Answer: C

Coarse particles are largely trapped in the nose and upper airways and cleared within hours, while fine particles reach the gas exchange region. The association with cardiovascular as well as respiratory mortality follows from that deep deposition.

Answer: D

Its high solubility means most of it is taken up before it reaches the deep lung, so bronchial constriction rather than alveolar damage is the characteristic effect. Asthmatics respond at concentrations that healthy people would scarcely notice at all.

Answer: A

Solubility governs where a gas is absorbed, and a poorly soluble gas passes the upper airways to reach the small airways and alveoli. That is why ozone damage appears deep in the lung while sulphur dioxide acts higher up.

Answer: B

Correct answer: Exposure magnitude to the effect seen

A dose-response relationship links the magnitude of exposure to the size of the effect observed - for instance a 6 per cent increase in mortality risk per 10 micrograms per cubic metre of PM2.5.

Establishing such a relationship is what turns an association into something usable: it allows the health burden of a given concentration to be estimated, and the benefit of a proposed reduction to be quantified in lives rather than in micrograms. The other options describe emission and dispersion relationships, which concern how the pollutant reaches the air rather than what it does once inhaled.

Answer: C

The London smog of 1952 produced thousands of excess deaths within days, which is the classic demonstration. Chronic effects such as reduced life expectancy from long-term particulate exposure are larger in total but far harder to observe.

Answer: D

Correct answer: Grazing animals

Fluoride is deposited on herbage downwind of aluminium smelters, brickworks and phosphate plants, and grazing animals ingest it with the forage over long periods. The result is fluorosis: mottled and brittle teeth, and painful bony exostoses that lame the animal.

Cattle are more sensitive than the vegetation itself, so damage appears in the herd before it appears in the pasture - which makes grazing livestock the effective receptor governing emission limits near such plants. Building stone, visibility and stratospheric ozone are affected by quite different pollutants.

Answer: A

Correct answer: Stippling of the leaf surface

Ozone enters the leaf through the stomata and oxidises the palisade mesophyll cells immediately beneath the upper surface, producing the characteristic fine stipple - small pale or bronze flecks on the upper leaf, with the veins unaffected.

The pattern distinguishes ozone injury from sulphur dioxide injury, which kills tissue between the veins in larger interveinal patches. Because ozone enters through open stomata, damage is greatest on well-watered plants in bright conditions - precisely when photosynthesis, and hence yield, is most active.

Answer: B

Correct answer: Interveinal necrosis

Sulphur dioxide dissolves in the moisture of the leaf and forms sulphite and then sulphuric acid, killing the mesophyll tissue between the veins while the veins themselves, better supplied, survive. The result is bleached or brown patches lying between green veins.

The contrast with ozone is diagnostic: ozone gives fine stippling on the upper surface, sulphur dioxide gives larger interveinal areas of dead tissue. Neither produces the root or stem symptoms offered as distractors, both being gases that enter through the stomata of the leaf.