| Date | November 2017 | Marks available | 4 | Reference code | 17N.2.SL.TZ0.3 |
| Level | Standard Level | Paper | Paper 2 | Time zone | Time zone 0 |
| Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
Figure 5: A layer of smog covering the Chilean city of Santiago
[Source: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=428144]
Identify one human factor that contributes to photochemical smog.
Identify one natural factor that contributes to photochemical smog.
Explain why the formation of photochemical smog may have harmful effects on the environment of cities such as Santiago (Chile).
Markscheme
(intensive) combustion of fossil fuels/organic matter/through high density traffic/urbanisation/industrialisation/forest burning/release of VOCs from aerosols;
local topography/high insolation/sunlight/low wind/thermal inversion;
reduced growth and productivity of plants/reduces crop yields by damaging them;
leads to the reduction of the air quality/visibility/ambience within the urban area;
particulates/chemicals within the smog enter the lungs and irritate respiratory system/cause respiratory disease/lung cancer;
particulates/chemicals within the smog may cause irritation of eyes/eye diseases;
the chemicals within the smog react with plastic/rubber causing it to perish/become hard/inflexible;
tropospheric ozone (a secondary pollutant) is a greenhouse gas/contributes to global warming/climate change;
smog pollutants reduce immune system of humans and animals (become more susceptible to diseases);
Award [1] for each correct explanation, up to [4 max].
Examiners report
Most were able to identify a valid human factor contributing to photochemical smog, though a good number mistakenly identified CO2 from fossil fuels.
A slim majority were able to identify one natural factor.
Vast majority were able to identify at least one impact of smog but very few identified four for full credit.
