Balancing Equations

Option E: Environmental ChemistryPrimary Air Pollution

http://www.cartoonstock.com/lowres/shr0702l.jpgSyllabus Statements: Exams 2009E.1.1 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. Include both natural and anthropogenic sources. Equations should be used as appropriate. E.1.2 Evaluate current methods for the reduction of air pollution. Examples include: COcatalytic converters NOxcatalytic converters, control of fuel/air ratio SOxalkaline scrubbing, limestone-based fluidized beds particulateselectrostatic precipitation VOCscatalytic converters. Main SourceFor todays PowerPoint: Unless otherwise noted, the information and diagrams come from the IB Chemistry Study Guide.Primary Air PollutantsSubstance not normally present in air, or a substance that is normally present, but in excess amounts.

Main primary air pollutants:carbon monoxide, COoxides of nitrogenoxides of sulfurparticulateshydrocarbonsCarbon MonoxideManmade Sources

Incomplete combustion of fossil fuels.

C8H18 + 17/2 O2 8 CO + 9 H2O

Carbon MonoxideNatural Sources

Incomplete oxidation of methane

CH4 + 3/2 O2 CO + 2 H2O

Carbon MonoxideEffects on Human Health

Prevents hemoglobin from carrying oxygen. Can lead to suffocation and death.

Unlike oxygen, CO does not release from the hemoglobin, and thus prevents oxygen from being carried.Carbon MonoxideMethods of Reduction

Use of lean burn engine, thermal exhaust reactor or catalytic converter.

Thermal Exhaust Reactor:2 CO + O2 2 CO2

Lean Burn Engine:Higher ratio of air:fuel, producing less CO. (Problem: Hotter temperatures produce more NOx)Carbon MonoxideMethods of Reduction

Use of lean burn engine, thermal exhaust reactor or catalytic converter.

Catalytic Converter: Catalyst of platinum, rhodium or palladium. Allows for complete oxidation of carbon monoxide. Also catalyzes the following reaction:2 CO + 2 NO 2 CO2 + N2Catalytic Converter

http://www.aa1car.com/library/converter.gifOxides of NitrogenWhat are they?

N2O, NO and NO2

Abbreviated NOxOxides of NitrogenManmade Sources

Created at high temperatures inside internal combustion engines.

N2 + O2 2 NO

Oxides of NitrogenNatural Sources

Electrical storms (lightning) and biological processes.

(Biological processes: Microbial action in wet tropical forests. http://www.epa.gov/nitrousoxide/sources.html)

Oxides of NitrogenEffects on Human Health

Respiratory irritant leading to respiratory tract infectionsOxides of NitrogenMethods of Reduction

Use of lean burn engine (????)Recirculation of exhaust gasesCatalytic ConverterLean Burn Engine?This produces two positive effects. First, the excess air reduces the temperature of the combustion process and this reduces the amount of oxides of nitrogen (NOx) produced by nearly half, compared to a conventional natural gas engine. Second, since there is also excess oxygen available, the combustion process is more efficient and more power is produced from the same amount of fuel.http://www.cumminspower.com/www/literature/technicalpapers/PT-7009-LeanBurn.pdfOxides of SulferWhat are they?

Primary Pollutant: SO2

SO2 can be oxidized in air to form SO3Oxides of SulfurManmade Sources

Combustion of sulfur- containing coal and smelting of sulfide ores

S + O2 SO2

Oxides of SulfurNatural Sources

Oxidation of H2S produced by volcanoes.Decay of organic matter

Oxides of SulfurEffects on Human Health

Respiratory irritant leading to respiratory tract infections

Oxides of SulfurMethods of Reduction

Removal of sulfur from fossil fuels before combustion.Alkaline scrubbingLimestone-based fluidized bed combustionRemoval of Sulfur from CoalSome sulfur present as metal sulfides (e.g. FeS)

Removed physically by crushing the coal and mixing with water. The more dense sulfides sink to the bottom and the cleaned coal can be skimmed off.Alkaline ScrubbingCaCO3 (s) + SO2 (g) CaSO3 (s) + CO2 (g)

CaO (s) + SO2 (g) CaSO3 (s)

2 CaSO3 (s) + O2 (g) + 4 H2O (g) 2 CaSO4.2H2O (s)

Scrubbing with an alkaline slurry of limestone (CaCO3) and lime (CaO). The resulting sludge is used for landfill or as gypsum to make plasterboard.Alkaline Scrubber

ParticulatesWhat are they?

Solid or liquid particles suspended in the air.ParticulatesManmade Sources

Burning of fossil fuels, particularly coal and diesel

ParticulatesNatural Sources

Soot, ash, dust, asbestos, sand, smoke, pollen, bacterial and fungal sporesParticulatesEffects on Human Health

Can affect the respiratory system and cause lung diseases, such as emphysema, bronchitis and cancer.ParticulatesMethods of Reduction

Electrostatic precipitation

The charged particulates are attracted to the oppositely charged electrode, which are shaken periodically so that the aggregated particulates fall to the bottom of the precipitator where they can be removed.

Electrostatic Precipitation

Volatile Organic CompoundsWhat are they?

CxHyR-H

HydrocarbonsManmade Sources

Unburned or partially burned gasoline and other fuels.Solvents. (e.g. paint thinner, finger nail polish remover)

HydrocarbonsNatural Sources

Plants, e.g. rice. Many plants emit unsaturated hydrocarbons called terpenes.HydrocarbonsEffects on Human Health

Some (e.g. benzene) are carcinogenic. Can form toxic secondary pollutants.HydrocarbonsMethods of Reduction

Catalytic converter.

Oxidizes unburned hydrocarbons.

CxHy + O2 CO2 + H2O