1. Environmental chemistry air pollution
Option E in Paper 3
study of the effect of human activity on the chemical processes in the environment
concerns political and natural borders
global issue
applied chemistry

2. Main topics: core air pollution acid deposition greenhouse effect
ozone depletion
dissolved oxygen in water
water treatment
soil
waste

3. Main topics: AHL
ozone depletion
smog
acid deposition
water and soil

4. Where is the air?

5. What is air?
Gas % N O
Ar 1
Water vapour 0-4 CO

6. How does the temperature change in the atmosphere?

7. Primary air pollutants
Substance that has harmful effect on environment
waste products from human activity
added directly to the air
pollutant = chemical in the wrong concentration
in the wrong place
primary air pollutants:
CO NOx particulates
SOx volatile organic compounds (VOCs)
Secondary – primary pollutants undergo chemical changes in the atmosphere

8. Air pollutants For each air pollutant you need to know:
sources: natural and man-made
(effects on health)
methods of reducing its emissions
any relevant balanced symbol equations

9. Carbon monoxide: sources
Natural:
atmospheric oxidation of methane
CH4 + 1/2O2  CO + 2H2
natural forest fires
Man-made: (anthropogenic)
incomplete combustion of carbon-containing fuels (fossil fuels); mainly in cities: localized problem as well as fluctuations during the day – rush hour
2C(s) + O2(g)  2CO(g)
forest fires
                
            

10. Carbon monoxide: health effect
CO combines with Fe in hemoglobin in blood more effectively than oxygen – therefore oxygen cannot bond onto hemoglobin
Less oxygen supplied to body cells
Effects:
headaches, dizziness
shortness of breath,
in case of high concentration : unconsciousness, death
Colorless and odorless so very dangerous

11. Carbon monoxide: reduction (1)
Lean burn engines: have controlled fuel injections which keep air/fuel ratio of 18 and produce low CO emissions.
Fuel ratios of 12.5 are usually produced for max power b/c it is rich in fuel and low in air. Need this fuel for engine to work properly. This increases the CO levels produced.
Combustion of octane:
2C8H18 (g) + 25O2 (g)  16CO2 (g) + 18H2O

12. Carbon monoxide: reduction (2)
Catalytic converter - hot gases mix with air and are passed over a platinum catalyst.
Two Types of Catalyst:
1. Oxidation catalyst – used in lean burn engines to convert CO to CO2.
2CO (g) + O2 (g)  2CO2 (g)
2. Three way catalyst – used in conventional engines to oxidize CO to CO2 and hydrocarbons to water. They also reduce NO to N2.
2NO (g) + 2CO (g)  2CO2 (g) + N2 (g)
Results in 90% reduction of pollution without loss of engine performance.

13. Catalytic converter

14. Carbon monoxide: reduction
Thermal Converters
Thermal Exhaust reactor – takes advantage of the heat of the exhaust gases and makes the CO react with more air to produce CO2. Any unburned volatile organic compounds such as hydrocarbon fuels are also oxidized to CO2 and H2O.
2CO (g) + O2 (g)  2CO2 (g)
CxHy + O2  xCO2 + y/2 H2O

15. Sulphur oxides: sources
Natural:
volcanoes (SO2)
sea spray
biological decay of organic matter which contains sulphur (veggies)
reduction of sulphates
Oxidation of hydrogen sulfide
2H2S + 3O2  2SO2 + 2H2O
Man-made:
coal-burning power stations
S(s) + O2  SO2
Smelting plants
Cu2S(s) + 2O2  2CuO + SO2

16. Sulphur oxides: sources
Sulfur trioxide –
Secondary pollutant formed in the atmosphere between the primary pollutant SO2 and O2. SO3 can dissolve in water to form sulfuric acid.
2SO2 (g) + O2(g)  2SO3(g)
H2O(l) + SO3(g)  H2SO4(aq)
Overall:
2H2O(l) + 2SO2(g) + O2  2H2SO4(aq)

17. Sulphur oxides: health effects
acidic oxides
lung irritants, affect in particular those suffering from respiratory problems e.g. asthma
formation of sulphuric acid aerosols (droplets of sulphuric acid) (often catalysed by metal particulates);
effects of aerosols:
irritant to the eyes
irritate vessels in lungs causing impaired breathing

18. Sulphur oxides: methods of reduction S can be removed before or after combustion
removal of SO2 from fumes before they are released:
Sulfur in coal can be removed by crushing it and washing with water.
Impurities in crude oil can be removed by mixing with KCO3 (basic):
H2S + CO3-  HS- + HCO3-

19. Sulphur oxides: methods of reduction S can be removed before or after combustion
removal of SO2 from fumes after they are released:
alkaline scrubbing:(wet scrubber) (also called flue gas desulphurization): an alkaline mixture is sprayed downwards into the exhaust gases.

20. Sulphur oxides: reduction
Wet scrubber

21. Sulphur oxides: methods of reduction S can be removed before or after combustion
Alkaline Scrubbing: 2 types
Mixture includes: CaO (lime) or CaCO3 (limestone)
CaO + SO2  CaCO3 (s)
CaCO3(s) + SO2  CaSO3(s) + CO2
2CaSO3 + O2  2CaSO4(s)
CaSO4 can be deposited in landfill or used to make plasterboard.
Mixture includes: MgO
MgO (s) + SO2(g)  MgSO3 (s)
MgO can be regenerated from the product (decomposition)
SO2 is used in the manufacturing of sulfuric acid.

22. Sulphur oxides: methods of reduction S can be removed before or after combustion
removal of SO2 from fumes after they are released:
Fluidized combustion: coal is mixed with powdered limestone on a metal plate. A strong air flow passes through the mixture from below and makes the particles of limestone and coal float above the plate making the mixture behave like a fluid.

23. Sulphur oxides: methods of reduction S can be removed before or after combustion
Fluidized combustion:
Heat produced from the combustion of coal causes CaCO3 to break up into CaO(s) and CO2
Sulfur dioxide is removed as it is formed in the combustion of coal. CaO reacts with SO2:
CaO + SO2  CaSO3
2CaO + SO2 + O2  2 CaSO4 (s)

24. Sulphur oxides: reduction
Limestone based fluidized bed

25. Nitrogen oxides: sources
NO, NO2, and N2O (causes photochemical smog and forms HNO3 (acid rain))
Natural:
Electrical storms release enough energy to cause oxidation of atmospheric nitrogen: N2 + O2  2NO (lightening)
Decomposition of organic matter containing nitrogen produces N2O
Man-made:
40% cars: N2 + O2  2NO (under high temp)
30% coal and oil power stations
20% burning fossil fuels
10% other
Photochemical smog is brown due to presence of NO2
2NO + O2  2NO2

26. Nitrogen oxides: health effects
choking irritating gas, affects eyes and people with respiratory problems
forms nitric acid aerosols/acid rain
nitric acid also increases the rate of oxidation of SO2
plays an important role in the formation of secondary pollutants e.g. ozone and smog

27. Nitrogen oxides: reduction
Three-way catalytic converter:
2CO + 2NO  2CO2 + N2
lean burn engines: high air/fuel ratio or low fuel/air
Recirculation of exhaust gases (EGR): nitrogen oxide emissions are reduced by reintroducing exhaust gases into the fuel mixture, lowering peak combustion temperatures as it is the high temperature in the combustion engine which causes nitrogen oxide production. Reduces NO emissions.

28. Particulates: sources
particulates = airborne/suspended liquid and solid particles (particles of C or dust) (particulates are polar and attract to water molecules and form aerosols)
Natural:
Sulfur from volcanic eruptions
large forest fires
Pollen, bacterial, and fungal spores
Man-made:
burning fossil fuels e.g. diesel
forest fires
industrial emissions; chemical processes
Incinerators
Arsenic from insecticides
Asbestos used in construction
Mercury from manufacturing of fungicides and paper

29. Particulates: health effects
particulates penetrate lungs and may block air passages
some are poisonous e.g. Pb and asbestos
adsorb chemicals and can act as catalysts in reactions producing secondary pollutants
by adsorbing also increase concentration and rate of reaction
reduce visibility

30. Particulates: reduction
Particulates and aerosols are removed naturally by rain and snow (gravitational settling)
Ways to prevent them from entering the atmosphere include:
Filtration, centrifugal separation, settling tanks, scrubbing, and electrostatic precipitation
Electrostatic precipitator: particulates are charged negatively and then attracted onto positively collection plates
Settling tanks: “dirty” air enters a chamber and dust will settle out by gravity .

31. Particulates: reduction

32. Volatile organic compounds: sources
Natural sources:
methane: bacterial anaerobic decomposition of organic matter (e.g. in rice paddies)
from plants e.g. terpenes
leakage from natural fossil reserves
Man-made:
evaporation of fuels
partial combustion of fuels
leakage from storage reservoirs
Solvents and paints

33. VOCs: health effects VOCs: reduction photochemical smog
can lead to carcinogenic compounds
fatigue, weakness
respiratory problems
VOCs: reduction
catalytic converter
Thermal exhaust reactor

34. Summary