Environmental chemistryEnvironmental 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

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

ozone depletion smog acid deposition water and soil

Where is the air?Where is the air?

How does the How does the temperature temperature

change in the change in the atmosphere?atmosphere?

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 particulates

SOx volatile organic compounds (VOCs)

Air pollutantsAir pollutantsFor 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

Carbon monoxideCarbon monoxide: sources Natural:

atmospheric oxidation of methane

CH4 + 1/2O2 CO + 2H2

natural forest fires

Man-made: incomplete combustion of carbon-containing

fuels; mainly in cities: localized problem as well as fluctuations during the day

forest fires

                

            

Carbon monoxideCarbon monoxide: health effect CO combines with Fe in haemoglobin in blood –

bonds 320 times stronger than oxygen – oxygen cannot bond onto heamoglobin

Less oxygen supplied to body cells Effects:

headaches, shortness of breath, in case of high concentration (e.g. rush hour):

unconsciousness, death

Carbon monoxide: reduction (1) Lean burn engines:

Decrease fuel /air ratio, for instance from 1:14.7 (stoichiometric ratio) to 1:18.

(or increase air /fuel ratio)

Carbon monoxideCarbon monoxide: reduction (2)Catalytic converter in car exhaust system:

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 contains sulphur reduction of sulphates

Man-made: coal-burning power stations (equation

starting from S in coal) roasting of metal sulphides e.g. ZnS

and Cu2S (equation)

Sulphur oxidesSulphur 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) (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 (1)

Wet scrubber

Sulphur oxidesSulphur oxides: reduction

Limestone based fluidized bed

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 nitrogen

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 eyes and

people with respiratory problems forms nitric acid aerosols/acid rain (equation

showing dissolution of nitric acid in water)

nitric acid also increases the rate of oxidation of SO2 (see later)

plays an important role in the formation of secondary pollutants e.g. ozone and smog

Nitrogen oxidesNitrogen oxides: reduction catalytic converter lean burn engines: high air/fuel ratio or low

fuel/air Recirculation/reburn 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 = airborne/suspended liquid and solid

particles Natural:

volcanic eruptions large forest fires

Man-made: burning fossil fuels e.g. diesel forest fires industrial emissions; chemical processes incinerators

ParticulatesParticulates: 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

ParticulatesParticulates: reduction Electrostatic

precipitator: particulates are charged negatively and then attracted onto positively collection plates

.

ParticulatesParticulates: reduction

Volatile organic compoundsVolatile organic compounds: sources: 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

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

VOCsVOCs: reduction catalytic converter