E1: Air Pollution Notes (UNMODIFIED)

Solutions: Controlling the amount of CO released in the exhaust of internal combustion engines in vehiclesMain points to remember: CO is a product of incomplete combustion Some approaches - focusing on ways to make more fuel (i.e. CO) react with oxygen 

Catalytic Converter:How it reduces CO: Hot gases released from the combustion of fuel = mixed with air Passed over catalyst (Platinum, Rhodium, Palladium) The 2 reactions that occur that reduce CO: Oxidation of CO to CO2 (CO + 1/2 O2 --> CO2) Reaction between CO and NO (2 CO + 2 NO --> 2 CO2 + N2) Pros:Effectively reduces COCons: Expensive to add equipment Requires unleaded fuel Contributes to the production of CO2

Lean Burn Engines:How it reduces CO: Adjusts the ratio of air to fuel in an engine The higher the ration of air: fuel, the more oxygen is available More complete combustion of the fuel (i.e. more CO2 than CO) Pros:  Reduces CO production Helps reduce the amount of VOC in vehicle exhaust Cons: Higher air: fuels and higher temperature promotes formation of NOx Higher air: fuel = reduced engine engines

Thermal Exhaust Reactor:How it reduces CO: Mix hot exhaust gases with more air Extra heat helps CO and unburned CxHy to burn completely to form CO2 and H2O Formulas: CO (g) + 1/2 O2 (g) --> CO2 (g) CxHy (g) + __ O2 (g) --> x CO2 (g) + y/2 H2O (l) Pros: Reduces CO and VOC production Less NOx produced than lean burn engines Cons:Expensive

Sources:Natural: 90%Main: Oxidation of Methane  Produced by the decomposition of organic materials in swamps and other areas when there is insufficient oxygen (i.e. incomplete combustion process) Formula: 2 CH4 (g) + 3 O2 (g) --> 2 CO (g) + 4H2O (l) Anthropogenic: 10%Main: Incomplete Combustion of Fossil Fuels (in vehicles, industries, etc.)Formula: C8H18 (g) + 17/2 O2 (g) --> 8 CO (g) + 9 H2O (l)

Sou

Sources:Natural: LimitedMain: Oxidation of H2S gas (from volcanoes and decomposing organic matterFormula: 2 H2S (g) + 3 O2 (g) --> 2 SO2 (g) + 2 H2O (l)Anthropogenic: Greatest ContributionMain: Burning of sulfur- containing fuelsCoal, smelting industries (purify metals from mined ores), Sulfuric acid manufacturing plants (produce SOx)

Primary VS SecondarySulfur Dioxide (SO2) = PRIMARY Sulfur impurities in low grade coal = react with oxygen during combustion reactions Released directly into the atmosphere S (s) + O2 (g) --> SO2 (g) Sulfur Trioxide (SO3) = SECONDARY Reacts with the oxygen in the atmosphere SO2 (g) + 1/2 O2 (g) --> SO3 (g)

SOLUTIONS: Pre-Combustion Removal of Sulfur From Fuels Post-Combustion Removal of Sulfur Dioxide from Exhaust

PRE-COMBUSTION REMOVAL OF SULFUR FROM FUELS Coal Washing - Sulfur (present as metal sulfides) physically removed [Cons: Difficult to remove all sulfur] Switching to higher grade form of coal (e.g. Anthracite) [Anthracite is scarce and expensive] Pros (for both): Reduces sulfur in coal pre-combustion

POST-COMBUSTION REMOVAL OF SULFUR DIOXIDE FROM EXHAUST Wet Alkaline Scrubbers Fluidized Limestone Beds

Wet Alkaline ScrubbersProcess: Burning of coal with sulfur impurities (CO2 + H2O + SO2) Wet Alkaline Mixture (CaCO3/ CaO/ Mg(OH)2 in water) sprayed onto gases Exhaust gas is free of SO2 and is composed of CO2 and H2O vapor Solid Calcium Sulfite and Magnesium sulfite that forms settles as "sludge" and can be used in other industrial processes (e.g. building materials) Formula involving Alkaline: CaCO3 + SO2 --> CaSO3 (s) + CO2 CaO + SO2 --> CaSO3 (s) Mg(OH)2 + SO2 --> MgSO3 (s) + H2O Pros:EffectiveCons: Expensive Build up of CaSO3 on scrubbers (therefore hard to maintain)

Fluidized Limestone BedsProcess: Coal with sulfur impurities is mixed with powdered CaCO3 Heat + Air (i.e. combustion) Reactions between SO2 and the decomposition products of CaCO3 Solid CaSO3 and CaSO4 are removed and reused Exhaust air is free of SO2 and is composed of CO2 and H2O vapor Formula: CaO + SO2 --> CaSO3 (s) 2 CaO + 2 SO2 --> 2CaSO4 (s) Pros:EffectiveCons:Exepnsive

Sour

Sources:Natural Sources (Limited) Nitrogen gas is very stable (due to triple bond), therefore needs high energy Therefore: lightning breaks nitrogen apart Soil bacteria may have enzymes to oxidize nitrogen gas Anthropogenic Sources Combustion of various fuels (have high enough energy) Majority = in internal combustion engines (as temperature may reach 1500˚C) Production of nitrogen oxides

Primary VS SecondaryNO = Primary Air Pollutant Produced when energy released by combustion process enables the reaction to occur N2 (g) + O2 (g) --> 2 NO (g) NO2 = Secondary Air Pollutant NO reacts with oxygen in the atmosphere to form NO2 (reddish brown gas) NO (g) + 1/2 O2 (g) --> NO2 (g)

Solution: Catalytic ConvertersHow it works:Platinum/ Palladium/ Rhodium catalysts in the catalytic converter of a vehicle's exhaust system undergoes reaction between CO and NO Formula Involved:2 CO (g) + 2 NO (g) --> 2 CO2 (g) + N2 (g)

Solution:Lean Burn EnginesHow it works:Adjusts air: fuel ratio (when low, less NO form, but promotes CO and VOC production)Compromise: 18:1 Ratio  Since engine performance = affected by air: fuel ratio

Solution:Recirculation of Exhaust GasesHow it works: Lower temperatures reduce formation of NOx If exhaust gas = recirculated back, then operating temperature decrease  Pros:Can effectively remove NOCons:Expensive Engines

Definition:non-polar organic compounds, vaporize easily and enter the air (Hydrocarbon = one example)

Sources:Natural Methane (from anaerobic decomposition of organic compounds) Terpenes (Unsaturated hydrocarbons found in resin (sap) of certain plants) Anthropogenic Unburned hydrocarbon (from incomplete combustion of fuels) , fuel spills Solvents used in cleaning products, construction materials, paints, industrial processes. etc

Solution: Catalytic ConverterHow it works: Catalysts in catalytic converters are also able to oxidize unburned hydrocarbon fuels Converts them into CO2 and H2O Formula:CxHy (g) + ___ O2 (g) --> x CO2 (g) + y/2 H2O (l)

Solution:Lean Burn EnginesHow it works: Using high Air:Fuel ratio help VOC to be oxidized more by fuel Reduce the amount of unreacted hydrocarbons present in the exhaust of vehicles

Definition:Solid particles of carbon or dust or very fine droplets of liquids, suspended in/ carried by the air

Sources:Natural Sandstorms Dust from natural Anthropogenic Soot (fine carbon particles) from incomplete combustion reactions [poorly maintained vehicles, diesel fuel burning engines, coal-burning power stations] Construction [production of dust during construction and release of asbestos from the demolition of older buildings insulated with asbestos] Burning of fields, forests, waste

Solution:Electrostatic PrecipitatorsHow it works:Most common and effective method for removing suspended solids from the airProcess: High voltage is used to produce strong electric field Particulates pass through charging section Electrons acculated on the solid particulates in the air is given a negative charge Air moves through collecting plates (positively charged) Negative particulates attracted to the positive plates (clean air moves out of precipitator) Pros:Effective (98% of particulates removed)Cons: Expensive Requires use of electricity

Carbon Monoxide

Sulfur Oxides

Nitrogen Oxides

Volatile Organic Compound

Particulates