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1、Air Pollution Inorganic Gaseous Pollutants,Major inorganic gaseous pollutants,Carbon monoxide (CO)Sulfur dioxide (SO2)Nitrogen Oxide (NO, NO2) NOx=NO+NO2Ozone (O3),HK 1-hour Air Quality Objectives for various air pollutants,a: 3-hr standard, b: annual arithmetic mean,Carbon monoxide: Health effect,C
2、O enters the blood stream and binds preferentially to hemoglobin, thereby replacing oxygen.,320 times stronger than hemoglobin-O2 binding,Carbon monoxide: sources and sinks,SourcesIncomplete combustion (internal engine)Biomass burningMethane oxidationOxidation of non-methane hydrocarbonDecay of plan
3、t matterSinkReaction with OH radical.OH + CO CO2 + H.H. + O2 + M HO2. + MRemoval by soil microorganism,Such as automobiles,CO formation from methane oxidation,CO emission sources in Hong Kong,Carbon monoxide: Atmospheric chemistry,CO + OH + O2 CO2 + HO2.HO2. + NO NO2 + OHNO2 + hv NO + OO + O2 + M O3
4、 + MNet: CO + 2 O2 + hv CO2 + O3,The net reaction can be viewed as a catalytic oxidation of CO to CO2. Net formation of O3 occurs.,Carbon monoxide: control strategies on the automobile source,Employ a leaner air/fuel mixture (higher air/fuel ratio)Employ catalytic exhaust reactorsExcess air is pumpe
5、d into the exhaust pipe.Air-exhaust mixture pass through a catalytic converter to oxidize CO to CO2.Addition of oxygenates to gasolineExamples of oxygenates: methanol, ethanol, MTBE,Sulfur dioxide: Health effect,Produce irritation and increasing resistance in the respiratory tract. Mucus secretionIn
6、 sensitive individuals, the lung function changes may be accompanied by perceptible symptoms such as wheezing, shortness of breath, and coughing. may also lead to increased mortality, especially if elevated levels of suspended particles are also present.,Sulfur dioxide: Sources and sinks,SourcesComb
7、ustion of S-containing fuel in electric power plants, vehicles.S (organic S + FeS2 pyrite) + O2 - SO2Oxidation of H2S: 2H2S + 3 O2 - 2 SO2 + 2 H2OH2S is produced as an end product of the anaerobic decomposition of S-containing compounds by micro organisms. Oxidation of DMSSink Converted into sulphur
8、ic acid in either gas or liquid phase,SO2 emission sources in Hong Kong,Formation of sulfuric acid and sulfate from SO2,In gas-phaseSO2 + .OH + M HOSO2. + MHOSO2. + O2 HO2. + SO3SO3 + H2O + M H2SO4 + M In aqueous phase, dissolved SO2 is oxidized to sulfate by O3(dominant pathway when pH5)H2O2 (domin
9、ant pathway when pH CaO + CO2, CaO + SO2 - CaSO3. CaSO3 is removed from the stack by an electrostatic precipitator.removal of S from smokestacks before entering the atmosphere. Flue-gas desulfurization: SO2 is washed from the chimney (flue) gases by absorption in an alkaline solution.,Sulfur dioxide
10、: Control strategies (Continued),3. DilutionInstallation of tall stacks reduces SO2 levels in the immediate neighborhood by dispersing them more widely,Nitrogen oxides: Health Effects,NOCellular inflammation at very high concentrations.May be incorporated into hemoglobin in the blood to interfere wi
11、th the transport of oxygen around the body.NO2irritate the lungs lower resistance to respiratory infection such as influenza.,Nitrogen oxides: Sources and sinks,SourcesFuel combustion in power plants and automobiles. N2 + O2 - NO2 NO + O2 - 2 NO2Natural sources: electrical storms; bacterial decompos
12、ition of nitrogen-containing organic matter,NOx emission sources in Hong Kong,Nitrogen oxides: Atmospheric chemistry,Interconversion of NO and NO2,NO2 + hv NO + O(1)O + O2 + M O3 + M(2)NO + O3 NO2 + O2(3),NO2 + hv NO + O(1)O + O2 + M O3 + M(2)HO2. + NO NO2 + OH(4)RO2. + NO NO2 + RO.(5),No net O3 for
13、mation,O3 is formed,Nitrogen oxides: Atmospheric chemistry,Formation of nitric acid,Gas-phase reactionNO2 + OH HNO3 daytime (dominate pathway),Heterogeneous reactionNO2 + O3 NO3 + O2NO3 + NO2 N2O5N2O5 + H2O (aq) 2 HNO3 (aq),Minor pathwayOnly operative during nighttime,Nitrogen oxides: Atmospheric ch
14、emistry,Formation of nitrate,HNO3 + NH3 NH4NO3HNO3 + NaCl(s) NaNO3 + HCl,Nitrogen oxides: Control strategies,1. Lower the combustion temperature of the furnace in electric power plants2. Install catalytic converters: catalytic converters in automobiles can remove 76% of NOx from tailpipes.,Two-stage
15、 combustion to reduce both NOx and VOCs,First stage: combustion conditionrich in fuelSecond stage: combustion conditionrich in air,Three-way catalytic converter for automobile exhaust (Remove CO, NO and HC),HC + H2O = H2 + CO2NO + 2H2 = N2 + 2 H2O,2CO + O2 = 2CO2HC + 2O2 = CO2 + 2H2O,Catalyst: Rhodium,Catalyst: Rhodium,Catalyst: Platium/palladium,
