Environmental Chemistry

Environmental Chemistry - 3/16/10 Environmental Chemistry...

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3/16/10 Environmental Chemistry **The 3 areas of the environment are mutually interrelated systems: air, water, and soil. E.1 I. Air Pollution a. Air is a mixture of nitrogen (78% ), oxygen (21%) , argon (1%), water vapor- humidity (1-4%), and carbon dioxide (0.04ppm) b. Pollutant - substance which has harmful effects on the environment; present at concentrations greater than natural levels as a result of human activities; their effect depends on their toxicity. b.i. Primary pollutants -emitted directly into the atmosphere : CO 2, CO, SO 2 , NO, VOCs (hydrocarbons) b.ii. Secondary pollutants- produced when primary pollutants undergo chemical change in the atmosphere. c. Carbon Monoxide (PP) - toxic because it affects oxygen uptake in the blood and binds to haemoglobin better than oxygen does, which prevents oxygen from being transported in the body; colorless/odorless. c.i. Anthropogenic sources - incomplete combustion of fossil fuels due to limited supply of oxygen and forest fires; slow atmospheric oxidation of methane c.ii. Natural sources - anaerobic decomposition of organic matter c.iii. Methods of Control- c.iii.1. Lean burn engines - control fuel injections with air:fuel ratio. Lower air:fuel ratios achieve maximum power but produces higher CO levels- 12.5 : 1 ratio c.iii.2. Catalytic converters - oxidize CO to CO 2; by helping reaction occur and add extra oxygen c.iii.3. Thermal convertors - uses heat from exhaust to react CO with air to produce CO 2 d. Nitrogen Oxides (PP)- NO, NO 2, N 2 O, which react with hydrocarbons to form photochemical smog and nitric acid (HNO 3 )- acid rain d.i. NO 2 is the most toxic (irritation of the eyes and respiratory problems) d.ii. Sources - d.ii.1. Anthropogenic - industrial burning of fossil fuels, motor vehicles, etc. d.ii.2. Natural - bacterial decomposition of N containing compounds produces NO and N 2 O lightning in the air. d.iii. MoC- d.iii.1. Lean burn - the conditions needed to oxidize CO to CO 2 promote production of nitrogen oxides. Lean burn which use an air: fuel ratio of 18.1 can be used to reduce emission of both. d.iii.2. Three Way Catalytic converters d.iii.3. Exhaust engine recirculation- re-circulates exhaust from engine to lower operating temps
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3/16/10 e. Sulfur Oxides- e.i. SO 2 e.i.1. Natural Sources - volcanoes, rotting vegetables; Secondary pollutant by oxidation of hydrogen sulfide e.i.2. Anthropogenic- fossil fuels, smelting plants, sulfuric acid plants e.ii. SO 3 e.ii.1. Secondary pollutant formed in atmosphere and reaction between PP sulfur dioxide and oxygen e.iii. MoC- e.iii.1. Pre-combustion methods- remove sulfur from coal beforehand e.iii.2. Post-combustion- e.iii.2.a. Alkaline scrubbing- mixture like calcium oxide or calcium carbonate added to exhaust gas to make calcium sulfate, which can be deposited into landfill or used to make plasterboard. e.iii.2.b.
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Environmental Chemistry - 3/16/10 Environmental Chemistry...

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