| Date | May 2022 | Marks available | 2 | Reference code | 22M.2.SL.TZ0.3 |
| Level | Standard Level | Paper | Paper 2 | Time zone | Time zone 0 |
| Command term | Outline | Question number | 3 | Adapted from | N/A |
Question
Figure 3: Concentration of atmospheric pollutants associated
with photochemical smog
[Source: Reprinted from Environmental Pollution and Control, fourth edition, J. Jeffrey Peirce, Ruth F. Weiner and P. Aarne
Vesilind, Chapter 18 – Air Pollution, Page 253, Copyright 1998, with permission from Elsevier (http://www.elsevier.com).]
Identify one primary pollutant from the pollutants shown in Figure 3.
Outline why the pollutant named in Question 3 (a)(i) is referred to as a primary pollutant.
Outline one reason why there is an increase in nitrogen oxides and hydrocarbons early in the day.
Explain the changes in ozone concentration over the period shown in Figure 3.
State one environmental impact of the accumulation of ozone shown in Figure 3.
Outline two local conditions that may increase the severity of photochemical smog.
Outline the role of catalytic converters in reducing photochemical smog.
Markscheme
NO/NO2/hydrocarbons;
impacts environment directly on emission / undergoes no chemical change before impacting environment / is active on emission;
Note: Even if response to 3(a)(i) is wrong full credit (ECF) can be given for appropriate definition of primary pollutant.
increase in fossil fuel combustion/increased traffic/transport/industry/power plants;
ozone is (a secondary pollutant) produced from nitrogen oxides/NOx reacting with oxygen;
it increases as more NOx accumulates in atmosphere due to human activity/fossil fuel use;
sunlight/heat catalyses this reaction so it increases towards midday;
later, ozone decreases due to dispersal by wind/less fossil fuel use/light becoming less intense;
Note: Do not credit any further detail of chemical process of ozone formation.
damages plants (crops and forests) / reduces photosynthesis/plant growth;
increase susceptibility to diseases/other pollutants;
habitat deterioration;
change in water and nutrient cycles;
loss of biodiversity;
impacts human health e.g. eye irritation/respiratory illness;
damages fabrics and rubber materials;
contributes to global warming/climate change / adverse weather;
Note: Do not credit responses that address ozone depletion.
low-lying topography/valley/mountains/high-rise buildings;
low windspeed/air movement;
thermal inversion / hot humid days;
high population density/heavy use of fossil fuels;
cities closer to equator get more intense sunlight;
conversion/reduction of nitrogen oxides/carbon monoxide/hydrocarbons from cars;
Examiners report
A surprising number misidentified ozone as a primary pollutant and showed a poor understanding of what is meant by a primary pollutant.
A surprising number misidentified ozone as a primary pollutant and showed a poor understanding of what is meant by a primary pollutant.
Most were able to link the early rise in nitrogen oxides and hydrocarbons with early use of vehicles and industries burning fossil fuels.
A quite significant proportion of candidates simply described the diurnal changes in ozone rather than offering underlying reasons for them.
Most were able to identify a clear impact of tropospheric ozone.
The majority were able to recognise high intensity of fossil fuel use as a local condition favouring photochemical smog but a smaller number could additionally identify geographical conditions.
The majority of candidates understood the general role of catalytic converters in reducing smog but few could give their detailed role in removing nitrogen oxides.
