Air Pollutants and Sources Questions and Answers

Answer: C

Correct answer: The fine fraction

The fine fraction, below 2.5 micrometres, combines the two properties that matter here. Its residence time of days to weeks allows transport over hundreds of kilometres, making it a regional rather than a local problem, and it penetrates to the alveolar region, where deposition drives the cardiopulmonary effects seen in chronic exposure studies.

Coarse particles settle within hours to days and deposit in the upper airways. Ultrafine particles penetrate furthest but coagulate within minutes to hours and contribute almost nothing to mass, so they neither travel far nor dominate the measured concentration.

Answer: D

Correct answer: An activity level in the matching units

An emission factor is useless on its own: it must be multiplied by an activity level expressed in the units the factor assumes. Tonnes of coal burnt for the first, vehicle kilometres for the second, tonnes of solvent throughput for the third, and head of livestock for the fourth.

Matching the units is the practical discipline - a factor in grams per kilometre cannot be applied to a count of vehicles without a distance. Ambient measurements, control efficiencies and meteorology all have their place elsewhere, but none is needed to build the inventory itself.

Answer: A

Correct answer: About 69 per cent

Divide the cooking exposure product by the daily total:

\[ \frac{3600}{5250} = 0.686 = 68.6\ \mathrm{per\ cent} \]

So three hours out of twenty-four account for more than two-thirds of the day's exposure, because concentration and duration multiply and the kitchen concentration is twenty times the outdoor level. This is why interventions are aimed at the cooking period specifically - a flue or an improved stove attacks the dominant term directly, whereas improving outdoor air would address less than a tenth of the total.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason gives both mechanisms. Photochemical ozone formation takes hours, during which the air mass carrying the precursors travels downwind - so the ozone appears where the air has gone, not where the emissions were.

Meanwhile, fresh nitric oxide in the city centre reacts with ozone and destroys it, a titration that suppresses ozone precisely where nitrogen oxide emissions are highest. Both effects push the maximum downwind, which is why rural stations often record the highest ozone of any in a region.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Because sulphur in the fuel oxidises almost completely to sulphur dioxide, essentially all of it appears in the flue gas, so the emission is proportional to fuel sulphur content.

Switching to a lower sulphur fuel therefore cuts the emission in proportion, and does so from the moment the new fuel reaches the burner - no equipment, no commissioning and no process change is needed. This is why fuel specification has been the fastest-acting sulphur control available to regulators.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Ammonia is the atmosphere's principal base, and it neutralises sulphuric and nitric acid to form ammonium sulphate and ammonium nitrate - both major constituents of fine particulate.

Since the ammonia and the acid precursors travel for hours to days before reacting, agricultural emissions from the countryside contribute measurably to urban PM2.5. This is why particulate policy in several countries now reaches into manure management and fertiliser application, sectors well outside the traditional air quality remit.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason is precisely why. Ozone is a secondary pollutant, formed in the atmosphere from oxides of nitrogen and volatile organic compounds in sunlight; nothing emits it, so there is no emission to limit.

Regulation therefore takes two other forms: an ambient standard on the concentration measured in the air, and emission limits on the precursors. The precursor route is complicated by the non-linear chemistry, in which cutting nitrogen oxides can raise ozone locally even while lowering it regionally.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the preference. Aerodynamic diameter is the diameter of a unit-density sphere with the same settling velocity, and it is exactly that combination of size, shape and density which determines how a particle settles, where it deposits in the lung, and whether a cyclone or impactor will capture it.

Physical diameter predicts none of those for a non-spherical particle of unusual density. This is why regulatory fractions such as PM10 and PM2.5, and the samplers that measure them, are defined aerodynamically.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Chlorofluorocarbons are inert in the troposphere and are removed only by photolysis in the stratosphere, so their atmospheric lifetimes run to many decades - about a century for CFC-12.

The stock already in the atmosphere therefore continues to deliver chlorine long after production stopped, and recovery of the ozone layer is expected only towards the middle of this century. It is a case of a successful treaty whose benefit is delayed by the physics rather than by any failure of compliance.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Fugitive emissions escape from many small openings - valve stems, flanges, seals, tank vents, transfer points - rather than through a single duct, so there is no flow whose rate and concentration can be measured.

They are therefore estimated instead, from leak detection surveys, component counts and tabulated factors, or by tracer and optical remote sensing techniques. That indirectness is exactly why fugitive terms carry the largest uncertainty in most industrial inventories.