Environmental chemistryEnvironmental chemistry study of the effect of human

activity on the chemical processes in

the environment concerns political and natural borders global issues 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

Environmental chemistryEnvironmental chemistryE1: air pollutionE1: air pollution Describe the main sources of carbon

monoxide (CO), oxides of nitrogen (NOx), oxides of sulfur (SOx), particulates and volatile organic compounds (VOCs) in the atmosphere.

Evaluate current methods for the reduction of air pollution.

the the atmosphereatmosphere

composition of dry clean airhttp://www.dep.state.pa.us/earthdaycentral/97/air_teachers/TAB1.htm

component content component content

  % by Vol. ppm   % by Vol. ppm

Nitrogen 78.09 780,900 Hydrogen .00005 0.5

Oxygen 20.94 209,400 Methane .00015 1.5

Argon .93 9,300 Nitrogen dioxide

.0000001 0.001

Carbon dioxide .0318 318 Ozone .000002 0.02

Neon .0018 18 Sulfur dioxide .00000002 0.0002

Helium .00052 5.2 Carbon

monoxide .00001 0.1

Krypton .0001 1 Ammonia .000001 0.01

Xeon .000008 0.08

Nitrous oxide .000025  

Units used to express amount of a gas % by volume ppm = parts per million/particles per million

particles Remember in gases, assuming conditions are

the same:

same volume = same number of particles So 78.09 % by volume is 78.09 % particles

per million particles or 780,900 ppm

primary air pollutantsprimary air pollutants waste products from human activity primary = 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 methods of reducing its emissions any relevant balanced symbol

equations

carbon monoxidecarbon monoxide: sources Natural:

atmospheric oxidation of methane

CH4 + ½ O2 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 – heavy traffic.

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 (in mass) from 1:14.7 (stoichiometric ratio/green band in diagram) to 1:18. Why?

(or increase air /fuel ratio to 18:1)

carbon monoxidecarbon monoxide: reduction (2)

catalytic converter in car exhaust system reduction of nitrogen oxide oxidation of CO and unburnt

hydrocarbons/VOCs

2CO (g) + O2 (g) 2CO2 (g)

 2NO (g) + 2CO (g) 2CO2 (g) + N2 (g)

 2C8H18 (g) + 25O2 (g) 16CO2 (g) + 18H2O (g)

Catalytic converter

catalytic converter

To achieve high rate of reaction for this redox process: exhaust gases are passed over platinum

which acts as a heterogeneous catalyst; converter has a honey comb structure to

increase surface area; very high temperature of the exhaust gases

also increase the rate of reaction dramatically.

Thermal exhaust reactorHeat from engine makes CO react with more air to oxidise it further to carbon dioxide.

sulphur oxidessulphur oxides: sources Natural:

volcanoes sea spray biological decay of organic matter that

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 sufferers

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 or removal of sulphur before burning coal/oil

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) (equations showing

reaction of CaO and Mg(OH)2)

Sulphur oxidesSulphur oxides: reduction (1)

Wet scrubber

Limestone based fluidised 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 in car engines and furnaces of power stations produces high

temperatures 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: sourcesparticulates = 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 given a negative charge 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