Effects of Air Pollution Questions and Answers

Answer: C

Correct answer: It affects only the area near the source

This is the false statement. Sulphur and nitrogen oxides must first be oxidised to sulphuric and nitric acid, which takes hours to days, and the air mass travels throughout - so deposition typically occurs hundreds or even thousands of kilometres downwind.

The other three are true: catchment geology determines vulnerability through buffering capacity, mobilised aluminium is what damages fish, and the acids derive from sulphur and nitrogen oxides. The long transport is what made acid deposition an international problem requiring treaty negotiation.

Answer: D

Correct answer: Reducing carbon monoxide emissions

Carbon monoxide is colourless and does not interact appreciably with visible light, so reducing it would not improve visibility at all.

The other three would. Primary particulate scatters light directly; sulphur dioxide is the precursor of sulphate aerosol; and ammonia is the base that neutralises sulphuric and nitric acid to form ammonium sulphate and nitrate - both in the 0.1 to 1 micrometre range that scatters most efficiently. Ammonia is easy to overlook precisely because it is not itself a particle.

Answer: A

Correct answer: Higher ground level ozone in cities

Ground level ozone is formed photochemically from nitrogen oxides and volatile organic compounds emitted at the surface, and it has nothing to do with the stratospheric layer. The two are the same molecule in different places, connected by name rather than by mechanism.

The genuine consequences of depletion follow from more ultraviolet B reaching the surface: increased skin cancer and cataract incidence in exposed populations, and reduced phytoplankton productivity in surface waters, with effects propagating up the marine food chain.

Answer: B

Correct answer: Wrong: black carbon absorbs and warms

The claim is wrong, and black carbon is the counterexample. It absorbs sunlight rather than scattering it, warming the atmosphere directly, and where it deposits on snow and ice it darkens the surface and accelerates melting.

Sulphate and most other scattering aerosols do cool, which is why the generalisation is tempting. The net effect of the whole aerosol burden is a balance between scattering and absorbing species, and quantifying it remains one of the larger uncertainties in climate projection.

Answer: C

Correct answer: It enters the stomata and damages leaf tissue

Ozone enters the leaf through the stomata and oxidises the mesophyll cells within, producing the characteristic stippling on the upper surface and impairing photosynthesis.

Because entry depends on open stomata, damage is greatest on well-watered plants in bright conditions - exactly when growth would otherwise be most vigorous. The effect on yield is far from negligible: 14 per cent in soybean and 9 in wheat at typical polluted-region exposures, across staple and cash crops alike. It cannot reach the roots, being a gas taken up by the leaf.

Answer: D

Correct answer: Peak ozone concentrations in the afternoon

Afternoon ozone peaks belong to photochemical smog, which is an oxidising phenomenon driven by sunlight acting on traffic emissions.

A sulphurous, or London-type, smog is the opposite in every respect: it is reducing rather than oxidising, composed of smoke and sulphur dioxide from coal burning, and it forms in cold, damp, stagnant winter conditions under an inversion. Acute excess mortality within days is its signature - some four thousand deaths in London in December 1952.

Answer: A

Correct answer: It is cleared from the lung within a few hours

This is the false statement. Fine particles deposit in the alveolar region, where there is no mucociliary escalator, so clearance depends on alveolar macrophages and takes weeks to months.

The other three are true, and the long residence explains two of them: prolonged contact with the gas exchange surface is what allows inflammatory and cardiovascular effects to develop. Its atmospheric residence time of days to weeks likewise allows transport over hundreds of kilometres, making fine particulate a regional problem.

Answer: B

Correct answer: The corrosion rate of galvanised steel in the city

Corrosion rate is a materials damage measure. It belongs in an economic assessment of pollution costs, but it contributes nothing to estimating a health burden.

The other three are exactly what a health impact calculation requires: the measured ambient concentration, the relative risk per unit concentration from epidemiology, and the population's baseline mortality rate. Multiplying the three gives the attributable deaths, which is how the benefit of an air quality improvement is expressed in lives.

Answer: C

Correct answer: Each unit is a tenfold change in acidity

pH is the negative logarithm to base ten of the hydrogen ion concentration, so each unit represents a factor of ten.

The consequence is that apparently small pH changes are large chemical ones: a fall from 6.5 to 4.5 is a hundredfold increase in acidity, enough to pass beyond the tolerance of most fish and to mobilise aluminium from catchment soils. Reading the scale as linear, or as a doubling per unit, badly understates what an acidification measurement means.

Answer: D

Correct answer: They absorb directly and lack a cuticle

Lichens have no roots and no waxy cuticle, so they take up water and nutrients - and any pollutants present - directly across their whole surface from the atmosphere. Nothing intervenes between the air and the living tissue.

They are therefore sensitive to sulphur dioxide at concentrations that leave higher plants unharmed, and because they are long-lived and slow-growing they integrate exposure over years. The result is the lichen desert around industrial centres and a well-established scale relating the species present to ambient sulphur dioxide.