1. Environmental Chemistry
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
smog
ozone
toxic substances in water

4. Air pollution

5. Air pollution

6. Primary air pollutants
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 SOx
particulates volatile organic compunds
(VOCs)

7. Air pollutants For each you need to know:
sources: natural and man-made
effects on health
methods of reduction
all relevant balanced equations

8. carbon monoxide: sources
Natural:
atmospheric oxidation of methane
natural forest fires
Man-made:
incomplete combustion of carbon-containing fuels (equation involving incomplete combustion of C and CH4 eg in car engines ) !!!!
forest fires
                           

9. Carbon monoxide emissions

10. Carbon monoxide: health effect
CO combines with Fe in haemoglobin in blood – bonds 320 x times stronger than oxygen
Less oxygen supplied to body cells
Effects:
headaches,
shortness of breath,
in case of high concentration (eg rush hour): unconsciousness, death

11. Carbon monoxide:

12. Carbon monoxide: reduction (1)
Lean burn engines: more air/less fuel (air:fuel of 18:1 or more)(stoichiometric is 14.7 :1)

13. Carbon monoxide: reduction (2)
Catalytic converter:
oxidation of CO and unburnt hydrocarbons
reduction of nitrogen oxide
equations:
2CO (g) + O2 (g)  2CO2 (g)
2NO (g) + 2CO (g)  2CO2 (g) + N2 (g)
2C8H18 (g) + 25O2 (g)  16CO2 (g) + 18H2O (g)

14. Catalytic converter

15. Sulphur oxides: sources
Natural:
volcanoes
sea spray
biological decay of organic matter which contain sulphur
reduction of sulphates
Man-made:
Coal-burning power stations (equation starting from S in coal)
Roasting of metal sulphides eg ZnS and Cu2S (equation)

16. Sulphur oxides: health effects
acidic oxides
lung irritants, suffering from respiratory problems eg asthma
formation of sulphuric acid aerosols (droplets of sulphuric acid) (equation) (often catalysed by metal particulates
effects of aerosols:
irritant to the eyes
irritate vessels in lungs causing impaired breathing

17. Sulphur oxides: methods of reduction
use of low-sulphur content fuels
removal of SO2 from fumes before they are released:
Limestone based fluidised bed (equations showing decomposition of calcium CaCO3 reaction of CaO with SO2)
Alkaline scrubbing(wet scrubber)(also called flue gas desulphurization): (equations showing reaction of CaO and Mg(OH)2)

18. Sulphur oxides:reduction
Wet
Scrubber
(uses
liquid)

19. Nitrogen oxides: sources
Natural:
electrical storms release enough energy to cause oxidation of atmospheric nitrogen: (equations showing oxidation of nitrogen and further oxidation of NO)
Decomposition of organic matter containing N
Man-made:
Combustion of fossil fuels produces enough heat to cause oxidation : (equation showing oxidation of nitrogen)

20. Nitrogen oxides: health effects
choking irritating gas, affects people with respiratory problems and eyes
forms nitric acid aerosols/acid rain (equation showing dissolution of nitric acid)
nitric acid also increases the rate of oxidation of SO2 (see later)
plays an important role in the formation of secondary pollutants eg ozone and smog

21. Nitrogen oxides: reduction
catalytic converter
lean burn engines
recirculation of exhaust gases: 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.

22. Particulates: sources
particulates = suspended liquid and solid particles
Natural:
volcanic eruptions
large forest fires
Man-made:
burning fossil fuels
forest fires
industrial emissions; chemical processes
incinerators

23. Particulates: health effects
particulates penetrate lungs and may block passages
some are poisonous eg Pb and asbestos
adsorb chemicals and can act as catalysts
by adsorbing also increase concentration and rate of reaction
reduce visibility

24. Particulates: reduction
Electrostatic precipitator: particulates are charged negatively and then attracted onto positively collection plates ( .

25. Particulates: reduction

26. Particulates reduction

27. Volatile organic compounds: sources
Natural sources:
methane: bacterial anaerobic decomposition of organic matter
from plants eg terpenes
leakage from natural fossil reserves
Man-made:
evaporation of fuels
Partial combustion of fuels
Leakage from storage reservoirs

28. Hydrocarbons: health effects
photochemical smog
can lead to carcinogenic compounds
fatigue, weakness
respiratory problems
Hydrocarbons: reduction
Catalytic converter

29. Dealing with current emissions
More use of public transport
Solar cars
Wind energy
Hydroelectric power
Hydrogen as a fuel

30. Ozone depletion O3 very pale bluish gas very powerful oxidising agent
pungent smelling odor
absorbs UV light
detection: [O3] in a sample of air can be measured using UV spectroscopy; the more UV is absorbed the more O3
in upper stratosphere; 15 to 45 km

31. Ozone depletion Two functions absorbs UV – 290 – 320 nm; UV
causes sunburn, skin cancer, eye cataracts
reduces plant growth, O3 destroys apparatus for photosynthesis
can cause genetic mutations
causes loss of plankton
Ozone production releases energy which produces an increase in temperature in stratosphere which gives it stability

32. Ozone: natural cycle (stratosphere)
formation of ozone:
O uv  O O (uv = 242 nm)
O O  O3
natural depletion of ozone
O O  2O2
O uv  O O (uv = 290 – 320 nm)
rate of formation = equal to rate of depletion
= steady state
both types of reactions are slow

33. Ozone: evidence for depletion
Antartica, autumn 2003
ozone hole = area having less than 220 Dobson units
(if 100 DU of ozone were brought to the Earth's surface, it would form a layer 1 millimeter thick)

34. Ozone: evidence of depletion

35. Ozone: depletion http://www.epa.gov/ozone/science/hole/size.html
                                                                                   
                                                                                   
                                                                                   

36. Ozone: man-made depletion
nitrogen oxides: sources: combustion, airplanes, nitrogenous fertilisers
CFCs = chlorofluorocarbons
used in: refrigerators, air conditioners, blowing agents, solvents, dry cleaning agents
chemically stable, low toxicity, volatile, insulating, fire suppressive, low cost
end up in stratosphere as they are not broken down
Cl free radical produced by uv - photodissociation
Cl acts as catalyst in ozone depletion – catalytic depletion

37. ChloroFluoroCarbons: useful compounds
chemically stable; long atmospheric life-time
low toxicity
low cost to manufacture
volatile liquids
cood solvents
insulating
fire-oppressive

38. Ozone: anthropogenic depletion

39. Ozone depletion: equations
photodissociation: C- Cl is weakest bond
CCl2F2  CClF2  Cl
catalytic depletion:   
Cl O3  ClO O2
  ClO + O  Cl  O2

40. Ozone depletion: alternatives to CFCs
propane and 2- methyl propane as refrigerant coolants: no halogens
fluorocarbons: stronger C-Hal bonds
hydrochlorofluorocarbons: hydrogen makes it more stable; fewer halogen free radicals released
hydrofluorocarbons: stronger C-F bond

41. Ozone depletion: alternatives to CFCs
Alternatives should still have other useful properties of CFS’s but
propane and 2- methyl propane as refrigerant coolants: greenhouse gases/flammable
fluorocarbons: greenhouse gases
hydrofluorocarbons: still some depletion