5.7 Urban Air Pollution
Learning outcome:
1) State the source and outline the effect of tropospheric ozone
2) Outline the formation of photochemical smog
3) Describe and evaluate pollution management strategies for urban air
pollution
Questions:
1) Define troposphere
2) What are the main sources of photochemical smog?
3) What are some possible impacts of photochemical smog on the environment?
4) Effects on human?
5) How is photochemical smog formed?
6) What is the difference between the summer smog and the winter smog?
7) Describe the air pollution in Mexico City case study
8) Evaluate pollution management strategies for air pollution in Mexico city
Answers:
5.7 Urban Air Pollution
- troposphere = lower atmosphere
- Main sources are road transport, solvent released from drying paints or inks,
and petrol handling and distribution
- Impacts: ozone damages crops and forests, irritates eyes, causes breathing
difficulties and my increase susceptibility to infection
- Effect on forests and crops: ground level ozone affects plant photosynthesis
and reduce crop yields
- Effects on humans: can harm lung tissues, impair the body's defense
mechanism, increase respiratory tract infection. Coughing, choking and sickness
increase, LR effects include premature aging of lungs. Increased risk of death
- Summer smog ozone is formed when nitrogen oxides and VOC react in the
sunlight. this takes hours, by which time the polluted air has drifted into
surroundings of suburban and rural areas. hence ozone pollution may be greater
outside the city centre
- Winter smog high levels of sulfur dioxide due to heating. under cold
conditions, vehicles work less efficiently, heating cars, releases larger amounts of
carbon monoxide. Urban at risk of winter smog as cold air sinks in from
surrounding hills
Case Study
Air pollution in Mexico City
Describe:
- average visibility has decreased from 100km to 1.5km
- levels of nitrogen dioxide increased,levels of ozone are twice as high
- carbon monoxide, ozone, sulfur dioxide, nitrogen oxide, hydrocarbons are air
pollutants
- intense sunlight turns these into photochemical smog, the smog prevents the
sun from heating the atmosphere enough to penetrate the inversion layer
blanketing the city
Strategies:
- reduce the use of private vehicles
- encourage use of public transport and carpooling
- control vehicles conditions: enforcement of engine maintenance standards
- change of fuels- reduction of lead and sulfur in fuels
Evaluation:
Strengths: 74% use public transportation, private only 25%, 30% of the cars are
more than 20 years old
Weakness: the population size and number o f cars, photochemical smog remain
a problem
5.8 Acid Deposition
Learning outcomes
1) Outline the chemistry leading to the formation of acidified
precipitations
2) Describe three possible effects of acid deposition on soil, water and
living organisms
3) Explain why the effect of acid deposition is regional rather than
global
4) Describe and evaluate pollution management strategies for acid
deposition
Questions:
1) What are the ions that form acid rain?
2) Outline the formation of acid rain
3) What are the possible effects of acid deposition
a) On soil?
b) On ecosystem?
c) On water?
d) On living organisms?
4) Why is the effect of acid deposition regional instead of global?
5) Explain why the rainfall in some parts of the world is unnaturally acidic.
6) What are some pollution management strategies for acid deposition? List at
least 5.
7) What are the strengths and limitations of the pollution management
strategies?
5.8 Acid Deposition
Ions that form acid rain are sulfate ions, nitrate ions and hydrogen ions.
Formation of acid rain: longer the oxides stay in the air, the greater chance they
will be oxidized to sulfuric acid and nitric acid. they dissolve in cloud droplets
(rain, snow, mist, hail) and reach the ground as wet deposition.
soil: soil acidification, reducing soil fertility and lowering pH, leaching of calcium
Water: excess nitrogen compounds cause eutrohpication, effect on fish
- living organisms: when fish from the water is eaten by people. can damage
plant membranes lead to plant death. interferes with photosynthesis.
- damages coniferous trees, losses its needles and will probably die. healthy:
needles last 7 years, with acid rain: 1-2 years
- areas with thin soils, lots of forest, streams, and lakes, high rainfall, downwind
of dense concentrations of fossil-fuel power stations are most affected by acid
rain
- burn less fossil fuel (need government initiative to switch to nuclear or hydropower)
- reduce number of private cars
- switch to low sulfur fuel
- remove sulfur before combustion
- allow decomposition of plants to return nutrients to the soil
-
expensive and time consuming to treat extensive areas already affected
by acid deposition