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UMD AOSC 621 - LESSON 25

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METO 621Air PollutionSlide 3Slide 4London Killer SmogSMOGSchematic of ozone production from VOCSlide 8StandardsOzone isopleths (NMHC vs NOx)Ozone vs NOx for NHMC=0.6 ppmcOverall scheme for air pollutionDispersion of acid rainThe acid scaleNatural levels of Acidity in RainSlide 16PowerPoint PresentationpH of precipitation over the USAcid rainSulfur Dioxide emissionsSlide 21NOx emission inventoryVOC EmissionsSlide 24Slide 25METO 621LESSON 25Air PollutionAir PollutionAir PollutionLondon Killer SmogSMOG•Word coined by Dr. Harold Des Veaux, a London physician in 1903. •SMOKE + FOG = SMOG•He meant London smog – sulfurous fumes from coal burning + large water droplets formed around smoke particles (soot)•1952 – Killer smog – 4000 deaths. Another episode in 1956 led to 1000 deaths.•In 1940 vegetable crop damage began to be seen in the Los Angeles basin•Haagen-Smit and colleagues showed that the effect was due to ozone – VOC and NOxSchematic of ozone production from VOCSMOG•NEEDS•Hydrocarbons and nitrogen oxides•Strong sunlight to start reactions•Warm temperatures to maintain reactions – the higher the temperature the faster the rate.•Peak ozone will be close to peak temperature – afternoonStandards•Ozone: 1-hour 125 ppbv*, 8-hour 85 ppbv–The 8-hour standard is much more stringent, and encompasses many areas where transport is the only issue (e.g Shenandoah National Park)•PM2.5: daily 65 g/m3, yearly 15 g/m3–Most areas will have trouble only with the annual standard•Visibility: a 60+ year glide path back to “natural conditions”*parts per billion by volumeOzone isopleths (NMHC vs NOx)Ozone vs NOx for NHMC=0.6 ppmcOverall scheme for air pollutionDispersion of acid rainThe acid scaleNatural levels of Acidity in Rain•Carbon dioxide dissolves in the rain dropCO2(g) + H2O(aq) ↔ H2CO3(aq)•Henry’s Law states that[H2CO3] = KHP(CO2)•KH = 3.4E-2 M ATM-1•In the liquid some of the H2CO3 ionizesH2CO3(aq) ↔ H+(aq) + HCO3-(aq)•This reaction has an equilibrium constant of 4.2E-7 M-3•For the overall reactionCO2(g) + H2O(aq) ↔ H+(aq) + HCO3(aq)The equilibrium constant Kc is 1.43E-8 M2.ATM-1Natural levels of Acidity in Rain)(]][[ where23COPHCOHKc−+=• in a liquid [H+] = [HCO3-] hence[H+]2 = KcP[CO2] given that CO2 has a mixing ratio of 320 ppm we get[H+] = 2.14E-6 and a pH of 5.67•pH of precipitation over the USAcid rain•Acid rain over the Eastern States is the highest – most of the sulfur containing coal occurs in this region•Shaded areas in the figure show where granite is found.•If the soil/rocks are carbonates (chalk, limestone) then the acid rain can be neutralized, and does not change the pH of the streams and lakes•If the soil/rocks are granite then acid rain is not neutralized, and can also leach out the heavy metals. Thus the pH of the lakes and streams can be lowered, and the heavy metal concentration raised.Sulfur Dioxide emissions67%17%4%3%2%7%Fuel Combustion- Electric UtilityFuel Combustion- IndustrialFuel Combustion- OtherMetalsProcessingNon-RoadVehiclesAll OtherNOx emission inventory28%13%5%30%19%5%Fuel Combustion- Electric UtilityFuel Combustion- IndustrialFuel Combustion- OtherOn-RoadVehiclesNon-RoadVehiclesAll OtherVOC Emissions33%7%29%13%18%SolventUtilizationStorage &TransportOn-RoadVehiclesNon-RoadVehiclesAll


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UMD AOSC 621 - LESSON 25

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