Transcript Lesson05
METO 621 CHEM LESSON 5 Air Pollution Air Pollution Air Pollution London Killer Smog SMOG • 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 NOx Schematic of ozone production from VOC SMOG • • • • 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 – afternoon Standards • 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 mg/m3, yearly 15 mg/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 volume Ozone isopleths (NMHC vs NOx) Ozone vs NOx for NHMC=0.6 ppmc Overall scheme for air pollution Dispersion of acid rain The acid scale Natural levels of Acidity in Rain • Carbon dioxide dissolves in the rain drop CO2(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 ionizes H2CO3(aq) ↔ H+(aq) + HCO3-(aq) • This reaction has an equilibrium constant of 4.2E-7 M-3 • For the overall reaction CO2(g) + H2O(aq) ↔ H+(aq) + HCO3(aq) The equilibrium constant Kc is 1.43E-8 M2.ATM-1 Natural levels of Acidity in Rain [ H ][ HCO3 ] where K c P(CO2 ) • 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 US Acid 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 emissions 2% 3% 4% 7% Fuel Combustion - Electric Utility Fuel Combustion - Industrial Fuel Combustion - Other 17% Metals Processing 67% Non-Road Vehicles All Other NOx emission inventory 5% 28% 19% Fuel Combustion - Electric Utility Fuel Combustion - Industrial Fuel Combustion - Other On-Road Vehicles 13% Non-Road Vehicles All Other 30% 5% VOC Emissions 18% Solvent Utilization 33% Storage & Transport 13% On-Road Vehicles Non-Road Vehicles 7% 29% All Other