Chapter FiveAir Pollution: Tropospheric Ozone, Inorganic Gaseous Pollutants, Particles1. Tropospheric OzonenGood Ozone and Bad OzonenTwo types of air pollutants: primary vs. secondarynFormation of ozonenNecessary ingredients for ozone formationnFormation of oxidants other than O3nPhotochemical smognPhotochemical air pollutionnControl strategies for ozoneGood Ozone and Bad OzonenStratospheric ozone protect lives on Earth from harmful effects of UV radiation. nTropospheric ozone:uCausing respiratory distress and eye irritation（呼吸困难和眼睛刺激）uDestroying plantsuProducing cracks in rubberOzone is a strong oxidant, reacts with molecules containing C=C double bonds, forming epoxides（环氧化物）.Two types of air pollutants: primary vs. secondarynPrimary pollutants: released directly from sourcesuExamples: CO, SO2, NOxnSecondary pollutants: formed through chemical reactions of the primary pollutants and the constituents of the unpolluted atmosphere in the air.uExample: O3Formation of ozoneNO2 + 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 formationO3 is formedNet of (1)+(2)+(4): RO2. + O2 O3 + RO. NO2 is capable of absorbing visible light ( SO2nOxidation of H2S: 2H2S + 3 O2 2 SO2 + 2 H2OuH2S is produced as an end product of the anaerobic decomposition of S- containing compounds by micro organisms. nOxidation of DMS（Dimethylsulfide）vSinkn Converted into sulphuric acid in either gas or liquid phaseSO2 emission sources in Hong KongFormation of sulfuric acid and sulfate from SO2nIn gas-phase SO2 + .OH + M HOSO2. + M HOSO2. + O2 HO2. + SO3 SO3 + H2O + M H2SO4 + M nIn aqueous phase, dissolved SO2 is oxidized to sulfate by uO3(dominant pathway when pH5)uH2O2 (dominant 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.研磨成粉Sulfur dioxide: Control strategies (Continued)3. DilutionInstallation of tall stacks reduces SO2 levels in the immediate neighborhood by dispersing them more widelyNitrogen oxides: Health EffectsNOnCellular inflammation（细胞炎症） at very high concentrations.nMay be incorporated into hemoglobin in the blood to interfere with the transport of oxygen around the body. NO2nIrritate（剌激） the lungs nlower resistance to respiratory infection such as influenza（流行性感冒）.Nitrogen oxides: Sources and sinksvSourcesnFuel combustion in power plants and automobiles. N2 + O2 NO 2 NO + O2 2 NO2nNatural sources: electrical storms; bacterial decomposition of nitrogen-containing organic matterNOx emission sources in Hong KongNitrogen oxides: Atmospheric chemistryInterconversion of NO and NO2NO2 + 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 formationO3 is formedNitrogen oxides: Atmospheric chemistryFormation of nitric acidGas-phase reactionNO2 + OH HNO3 daytime (dominate pathway)Heterogeneous reaction NO2 + O3 NO3 + O2 NO3 + NO2 N2O5 N2O5 + H2O (aq) 2 HNO3 (aq) Minor pathwayOnly operative during nighttimeNitrogen oxides: Atmospheric chemistryFormation of nitrateHNO3 + NH3 NH4NO3HNO3 + NaCl(s) NaNO3 + HClNitrogen oxides: Control strategies1. Lower the combustion temperature of the furnace in electric power plants 2. Install catalytic converters: catalytic converters in automobiles can remove 76% of NOx from tailpipes.Two-stage combustion to reduce both NOx and VOCsnFirst stage: combustion conditionrich in fuelnSecond stage: combustion condition rich in airThree-way catalytic converter for automobile exhaustHC + H2O = H2 + CO2NO + 2H2 = N2 + 2 H2O2CO + O2 = 2CO2HC + 2O2 = CO2 + 2H2OCatalyst: RhodiumCatalyst: RhodiumCatalyst: Platinum/palladium(Remove CO, NO and HC)NOx control in power plantsnAmmonium reduction of NOu4NH3 + 6NO = 5 N2 + 6 H2OnUrea（尿素） reduction of NOu2CO(NH2)2 + 6NO = 5 N2 + 2 CO2 + 4 H2O3. Particles in the AirAir quality and particles Health effects Impact in ecosystems Climatic change Visibility decreaseAir quality and particlesnEpidemiological (流行病学) evidence associates atmospheric particles with diseases and mortality.uParticles penetrate the lungs, blocking and irritating air passages.uParticles themselves could exert toxic effects. (toxic substances present in the particles) Polycyclic Aromatic Hydrocarbons are examples of toxic substances in aerosols.TermsnTSP: Total suspended particulate matternRSP: Respirable suspended particulate matternPM10: Particulate matter of less than 10 m; equivalent to RSP.nPM2.5: Particulate matter of less than 2.5 mTermsHealth effectsDivided into Thoracic and Non-Thoracic ParticlesThoracic Particles Divided into Fine and Coarse ParticlesFine particles divide