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METO 637

METO 637. LESSON 18. 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.

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METO 637

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  1. METO 637 LESSON 18

  2. Schematic of ozone production from VOC

  3. 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

  4. 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

  5. Ozone isopleths (NMHC vs NOx)

  6. Ozone vs NOx for NHMC=0.6 ppmc

  7. Daily Ozone Cycle Ozone production follows a daily cycle with maximum concentrations typically observed in the late afternoon. This cycle is a signature of the dynamic processes of atmospheric air pollution Ozone Concentration Sunrise Sunset Time of day

  8. Comparison of ozone data at Fort Meade for August 2 and 8 2002

  9. Overplot of 2 and 8 Aug 2002 and the difference between the two days

  10. Difference 2 Aug minus 8 Aug*1.2

  11. Back Trajectories, Hysplit AUG 2, 2002 AUG 8, 2002

  12. Comparison of Aug 2 and 8, 2002 • Ozone data for August 8 is typical for local pollution on a clear warm day. • The NOx and VOC are emitted early in the morning and the ozone amount slowly increases as the temperature increases. The peak production is at about 3-4 in the afternoon when the temperature at the ground is a maximum. • The back trajectory shows fast upper level winds, which start at a high altitude and then subside to boundary levels at Baltimore. • Small probability of upper air being polluted.

  13. Comparison of Aug 2 and 8, 2002 • On the 2nd of August the back trajectories show that the air is moving slowly at the boundary layer, and the probability of this air being polluted is high. • The nocturnal inversion typically breaks down at about 10-11 in the morning. • Hence the peak in ozone at this time must come from downward transport. • The overall shape of the ozone data on Aug 2 is a combination of locally produced ozone peaking at about 3 pm and a downward movement of ozone from above at about 10.00 am. • This ozone above the boundary layer is yesterday’s ozone • The winds above the boundary layer are usually high. Hence the ozone has been transported some distance

  14. 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

  15. Natural levels of Acidity in Rain • 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

  16. Dispersion of acid rain

  17. pH of precipitation over the US

  18. 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.

  19. Sources of pollutants in the USA

  20. Sulfur Dioxide emissions

  21. Flight area Annual mean haze, United States IMPROVE network

  22. Detection Techniques • In situ via UV pulsed fluorescence. • Modified commercial instrument • Detection limit ~70 ppt () • Response time ~3 min • Satellite via UV (315 to 327 nm ) spectroscopy (modified DOAS)

  23. Scale height ~1.1 km

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