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

Main topics: AHLMain topics: AHL smog ozone toxic substances in water

Air pollutionAir pollution

Air Air pollutionpollution

Primary air pollutantsPrimary 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 pollutantsAir pollutantsFor each you need to know:

sources: natural and man-made effects on health methods of reduction all relevant balanced equations

carbon monoxidecarbon 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 monoxideCarbon 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 monoxideCarbon 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 monoxideCarbon 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 oxidesSulphur 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 oxidesSulphur 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 oxidesSulphur 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 oxidesSulphur oxides:reduction

Wet Scrubber (uses liquid)

Nitrogen oxidesNitrogen 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 oxidesNitrogen 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 oxidesNitrogen 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.

ParticulatesParticulates: 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

ParticulatesParticulates: 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

ParticulatesParticulates: reduction Electrostatic precipitator: particulates are charged

negatively and then attracted onto positively collection plates (http://www.eas.asu.edu/~holbert/wise/electrostaticprecip.html).

ParticulatesParticulates: reduction

ParticulatesParticulates reduction

Volatile organic compoundsVolatile organic compounds: : sourcessources

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

HydrocarbonsHydrocarbons: health effects photochemical smog can lead to carcinogenic compounds fatigue, weakness respiratory problems

HydrocarbonsHydrocarbons: reduction Catalytic converter

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

Ozone depletionOzone 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 depletionOzone depletionTwo 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: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:Ozone: evidence for depletionAntartica, 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)

OzoneOzone: evidence of depletion

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

                                                                           

        

                                                                           

        

                                                                           

        

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

OzoneOzone: anthropogenic depletion

Ozone depletionOzone depletion: equations photodissociation: C- Cl is weakest bond

CCl2F2 CClF2 + Cl

catalytic depletion:   

Cl + O3 ClO + O2

 

  ClO + O Cl + O2

Ozone depletion: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: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