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

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

Main topics: AHL smog ozone toxic substances in water

Air pollution

Air pollution

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)

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

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                            

Carbon monoxide emissions

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

Carbon monoxide:

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

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)

Catalytic converter

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)

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

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)

Sulphur oxides:reduction Wet Scrubber (uses liquid)

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)

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

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.

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

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

Particulates: reduction Electrostatic precipitator: particulates are charged negatively and then attracted onto positively collection plates (http://www.eas.asu.edu/~holbert/wise/electrostaticprecip.html) .

Particulates: reduction

Particulates reduction

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

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

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

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

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

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

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)

Ozone: evidence of depletion

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

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

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

Ozone: anthropogenic depletion

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

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

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