Air Pollutants and Sources Questions and Answers

Answer: A

Correct answer: A is false but R is true

The assertion is false. An inventory is not inherently more accurate than a monitoring network - it is an estimate built on activity data and generic factors, and its uncertainty can be large where the factors do not match local conditions or where fugitive sources dominate.

The reason is true and describes the method, but the method is precisely the source of the uncertainty. The two tools are complementary rather than competing: the inventory says where the emissions come from and what a control measure would do, while monitoring says what is actually in the air. Discrepancies between them are how both get improved.

Answer: B

Correct answer: 1 and 2 only

Statement 1 is correct: at ground level ozone is a secondary pollutant, formed from oxides of nitrogen and volatile organic compounds in sunlight. Statement 2 is correct: in the stratosphere the same molecule absorbs biologically damaging ultraviolet radiation and is essential.

Statement 3 is false. No vehicle emits ozone - exhausts emit its precursors. Indeed fresh nitric oxide from exhausts destroys ozone near the road, which is why kerbside ozone is often lower than at a background site.

Answer: C

Correct answer: 1 and 2 only

Statement 1 is correct: PM2.5 is the fraction with aerodynamic diameter below 2.5 micrometres. Statement 2 is correct: fine particles penetrate to the alveolar region, which is why they drive the cardiopulmonary effects.

Statement 3 is false and reverses the comparison. Fine particles have the longer residence time - days to weeks - because they are too small to settle appreciably and too large to coagulate quickly. Coarse particles settle out within hours to days, which is why fine particulate is a regional problem and coarse particulate a local one.

Answer: D

Correct answer: 1 and 2 only

Statement 1 is correct: point sources such as power station and kiln stacks are treated individually, with their location, height and gas conditions recorded. Statement 2 is correct: area sources are described by an emission density per unit area, because their individual emitters are too numerous to enumerate.

Statement 3 is false. An emission factor gives emitted mass per unit of activity; it says nothing about permitted ambient concentration, which is set by an air quality standard at the other end of the chain entirely.

Answer: A

Correct answer: 1 and 2 only

Statement 1 is correct: thermal NOx forms from atmospheric nitrogen and oxygen at high flame temperature, by the Zeldovich mechanism. Statement 2 is correct: fuel NOx arises from nitrogen chemically bound in the fuel, and matters for coal and heavy oil rather than for gas.

Statement 3 is false and inverts the dependence. Lowering the peak flame temperature decreases thermal NOx, sharply, which is exactly why staged combustion, flue gas recirculation and low-NOx burners all work by suppressing the peak temperature.

Answer: B

Correct answer: A-2, B-1, C-4, D-3

Each pollutant is matched to its dominant source. Sulphur dioxide (A) comes from combustion of sulphur-bearing coal and oil (2); ammonia (B) from livestock manure and fertiliser application (1), which supply 80 to 90 per cent of the total in most countries.

Carbon monoxide (C) comes from incomplete combustion in engines and stoves (4), and chlorofluorocarbons (D) from legacy refrigeration and aerosol propellant use (3) - legacy because production has been phased out, yet the long-lived stock continues to reach the stratosphere.

Answer: C

Correct answer: A-2, B-1, C-4, D-3

Each pollutant is matched to its principal effect. PM2.5 (A) causes cardiopulmonary disease and reduces visibility (2); sulphur dioxide (B) drives acid deposition (1) after oxidation to sulphuric acid.

Chlorofluorocarbons (C) deplete stratospheric ozone (4), releasing chlorine when photolysed. Methane (D) is a climate forcer and, through its role in tropospheric chemistry, raises background ozone (3) - the one item on the list whose effect is global and long-term rather than regional.

Answer: D

Correct answer: A-2, B-1, C-4, D-3

Each source takes its inventory classification. A power station stack (A) is a point source (2), a single identified location with known height and gas conditions. An arterial road (B) is a line source (1).

A residential district (C) is an area source (4), described by an emission density because its thousands of individual emitters cannot be enumerated. Leaking refinery flanges (D) are fugitive emissions (3) - escaping other than through a stack, and therefore estimated from leak surveys rather than measured.

Answer: A

Correct answer: A-2, B-1, C-4, D-3

Each term takes its standard definition. Aerodynamic diameter (A) is the diameter of a unit-density sphere with the same settling velocity (2). An emission factor (B) is emitted mass per unit of activity (1).

A secondary pollutant (C) is one formed by reaction in the atmosphere (4), and global warming potential (D) is a substance's climate effect relative to carbon dioxide over a stated period (3) - the stated period being essential, since methane's value is about 28 over a hundred years but around 80 over twenty.

Answer: B

Correct answer: Ground level ozone

Ground level ozone is secondary, not primary. Nothing emits it: it is formed in the atmosphere when oxides of nitrogen and volatile organic compounds react in sunlight, which is why it peaks in the afternoon and downwind of the city whose traffic supplied the precursors.

The other three are primary, leaving their source in the form in which they are measured - particulate from a stack, sulphur dioxide from burning sulphur-bearing fuel, and carbon monoxide from incomplete combustion. Only a primary pollutant can be given an emission limit.