Giáo trình Hóa học môi trường Không khí - Nguyễn Thanh Hải

Nội dung text: Giáo trình Hóa học môi trường Không khí - Nguyễn Thanh Hải

1. HÓA HỌC MÔI TRƯỜNG KHÔNG KHÍ GV: ThS. NGUYỄN THANH HẢI Bài giảng cho lớp MT K30
2. TẦNG OZONE ThS. Nguyễn Thanh Hải
3. TẦNG OZONE ThS. Nguyễn Thanh Hải
4. TẦNG OZONE ThS. Nguyễn Thanh Hải
5. Cơ chế tạo thành ozone O2 + hn 2O O2 + O + M O3 + M O2 + O + M O3 + M 3O2 +hn 2O3 Sự phân hủy ozone tự nhiên O3 + hn O + O2 O3 + O 2O2 2O + hn 3O ThS. Nguyễn Thanh Hải 3 2
6. Các tia UV • UVA: 320 – 400 nm • UVB: 290 – 320 nm • UVC: <290 nm ThS. Nguyễn Thanh Hải
7. TẦNG OZONE ThS. Nguyễn Thanh Hải
8. TẦNG OZONE a) O2+ hv ( 2O b) O+O2+M -> O3+M c) O3 + hv (<320nm) O +O2 d) O + O3 2O2 M là một phân tử khí trong khí quyển (O2 hoặc N2) ThS. Nguyễn Thanh Hải
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11. Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải
12. Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải
13. Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải
14. Phổ hấp thu của DNA Tia UV làm các phân tử DNA tham gia các phản ứng quang hóa ThS. Nguyễn Thanh Hải
15. Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải
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17. TẦNG OZONE . • Hydroxyl ( OH) . . OH + O3 = HO + O . . 2 2 HO2 + O = OH + O2 O + O3 = 2 O2 • Chlorine và bromine (Cl và Br) . . Cl + O = ClO + O . 3 . 2 ClO + O = Cl + O2 O + O3 = 2 O2 • Nitric oxide (NO) NO + O3 = NO2 + O2 NO2 + O = NO + O2 O + O3 = 2 O2 ThS. Nguyễn Thanh Hải
18. TẦNG OZONE ThS. Nguyễn Thanh Hải
19. Ảnh hưởng của sự suy giảm ozone • Vùng UV-B mở rộng tới vùng UV-C khiến ozone không thể loại bỏ hết các tia UV ThS. Nguyễn Thanh Hải
20. Effect of Ozone Depletion • The UV-B region will expand as there will be insufficient ozone to remove all the UV • light1-2% increase in skin cancer for each 1% decrease in ozone • Currently, one in five Americans will develop skin cancer Basal cell carcinoma in their lifetime ThS. Nguyễn Thanh Hải
21. Causes of Ozone Depletion • Naturally, ozone is continually formed and destroyed by light Formation 3O2 +hn 2O3 • This results Removal in a steady2O3 +state hn concentration3O2 of ozone in the stratosphere • There are minor depletion reactions caused by other stratospheric gases including water vapor, nitrogen oxides, ThS. Nguyễn Thanh Hải methane, and methyl bromide (produced
22. Anthropogenic Ozone Depletion • Human activity increases the amount of naturally occurring methane and nitrogen oxides in the stratosphere • The major causes are photochemical decomposition of chlorinated and brominated CFCl3 (CFC-11) hydrocarbons ThS. Nguyễn Thanh Hải
23. Anthropogenic Ozone Depletion • Ultraviolet light causes photochemical breakdown, releasing Cl or Br free radicals ThS. Nguyễn Thanh Hải
24. Anthropogenic Ozone Depletion • The mechanism of the reaction is a typical free radical reaction  CFCl3 + hn CFCl2· + Cl·  Cl· + O3 ClO· + O2  ClO· + ·O O2 + Cl· • A free radical can only be destroyed by reaction with another free radical • Steps 2 and 3 in the mechanism form a cycle, so one atom of Cl produced in step 1 can destroy many thousands of O3 ThS.molecules Nguyễn Thanh Hải
25. Anthropogenic Ozone Depletion • The ultimate fate of the Cl atom may be to react with CH4 Cl· + CH4 CH3· + HCl • HCl eventually washes out into the troposphere, but it acts as a reservoir of Cl atoms that is the cause of the polar • Theozone CFCl holes2· probably continues to be photolysed to produce more free chlorine CFCl2· + hn CFCl + Cl· ThS. Nguyễn Thanh Hải
26. Polar Ozone Depletion • The polar ozone holes are caused by a different mechanism, in which polar stratospheric clouds of nitric acid trihydrate act as a catalytic surface for the reaction of chlorineThS. Nguyễn Thanh carriers Hải (HCl and ClONO )
27. Lifetimes of CFC’s • One of the primary problems with CFC’s is that they do not react in the troposphere, so can diffuse into the stratosphere for a CFC-11 very long timeTrichlorofluoromethane (45 years) CFC-115 Monochloropentafluoroethane (1700 years) • Adding hydrogen to the molecule dramatically speeds up its decompositionHCFC -in21 the troposphere Dichlorofluoromethane (2 years) ThS. Nguyễn Thanh Hải
28. The Montreal Protocol • Originally ratified in 1987, it has been amended 5 times (1990, 1992, 1995,  1997,Only 12 1999) countries have not ratified this treaty •Equatorial Guinea •Afghanistan •Iraq •Andorra •Eritrea •Bhutan •Niue •Holy See •Guinea-Bissau •Cook Islands •East Timor •San Marino • Limitations on the use of CFC’s in aerosol containers began voluntarily in the 1970’s • CFC’s have not been used in aerosols in Canada since mid 1980’s (exception some ThS.medical Nguyễn Thanh Hảiinhalers until 2005)
29. The Montreal Protocol • Phaseout of production of Class I ozone depleting substances by 1995  chlorofluorocarbons  halons  carbon tetrachloride  methyl chloroform  hydrobromofluorocarbons  methyl bromide (2005) • Phaseout of production of Class II HCFC’s by 2030 ThS.by Nguyễn developed Thanh Hải nations
30. The Canadian Picture  We have dramatically reduced our consumption of ozone depleting substances. ThS. Nguyễn Thanh Hải
31. The Future • Although no longer allowed, there are still large amounts of CFC’s in already produced goods. ThS. Nguyễn Thanh Hải
32. The Future • Although no longer allowed, there are still large amounts of CFC’s in already produced goods. It is estimated that the ozone layer will not return to its pre-1980 level until at least 2050. ThS. Nguyễn Thanh Hải
33. The Greenhouse Effect • A misnomer, since the way the atmosphere retains heat has little to do with the way a greenhouse actually works. • Greenhouses prevent convection. The atmospheric greenhouse effect ThS. Nguyễnworks Thanh Hải by
34. Historical Background • Joseph Fourier (1768–1830) studied the role of solar • radiationJohn Tyndall (1820– 1886) in 1859 emphasized the role of water vapor • Svante Arrhenius (1859 - 1927) emphasized the role played by carbon ThS. Nguyễn Thanh Hải dioxide
35. How the Greenhouse Effect Actually Works • The sun is a blackbody radiator with a temperature of about 5700 K ThS. Nguyễn Thanh Hải
36. How the Greenhouse Effect Actually Works • Gases in the earth’s atmosphere absorb energy where they have allowed quantumThS. Nguyễn Thanh Hải transitions
37. How the Greenhouse Effect Actually Works • Gases in the earth’s atmosphere absorb energy where they have allowed quantumThS. Nguyễn Thanh Hải transitions
38. How the Greenhouse Effect Actually Works • Direct absorption of solar radiation contributes very little to atmospheric heating ThS. Nguyễn Thanh Hải
39. How the Greenhouse Effect Actually Works • There is a steady state between the amount of solar radiation the earth receives, and what it re- radiates back into space ThS. Nguyễn Thanh Hải
40. How the Greenhouse Effect Actually Works • About 70% of the sun’s irradiation reaches the earth’s surface (surface albedo) ThS. Nguyễn Thanh Hải
41. How the Greenhouse Effect Actually Works • About 70% of the sun’s irradiation reaches the earth’s surface • The(surface average albedo) temperature of the earth is about 15 ºC (288 K) ThS. Nguyễn Thanh Hải
42. How the Greenhouse Effect Actually Works • The earth re- radiates as a black body radiator at a much lower temperature than the sun ThS. Nguyễn Thanh Hải
43. How the Greenhouse Effect Actually Works • A very large part of this energy is absorbed by water vapor in the earth’s atmosphere ThS. Nguyễn Thanh Hải
44. How the Greenhouse Effect Actually Works • A much smaller amount of the earth’s radiant energy is absorbed by CO2 ThS. Nguyễn Thanh Hải
45. How the Greenhouse Effect Actually Works • CO2 is important as it absorbs strongly in a region where water does not ThS. Nguyễn Thanh Hải
46. How the Greenhouse Effect Actually Works • OtherThere gasesis a large alsoatmospheric window in contributethe visible, to and a much makesmaller up one the in the totalinfrared absorption spectrum of the earth’s atmosphereThS. Nguyễn Thanh Hải
47. How the Greenhouse Effect Actually Works • The net result is that the earth’s atmosphere is warmer because it absorbs the infrared energy radiated by the earth ThS. Nguyễn Thanh Hải
48. How the Greenhouse Effect Actually Works • A 235 W/m2 radiating black body would have a temperature of - • 18Since ºC the earth’s actual average temperature is about 15 ºC, the greenhouse effect contributes ThS. Nguyễn Thanh Hải approximately 33 º
49. Greenhouse Gases • Water vapor is by far the most important greenhouse gas ThS. Nguyễn Thanh Hải
50. Greenhouse Gases • Animal respiration and oceanic evaporation release 150 billion T of CO2 per year • Anthropogenic sources – Carbon dioxide is the most important anthropogenic greenhouse gas (7 billion T per year) – Primary source is from combustion C8H18 + 25/2 O2 8 CO2 + 9 ThS.H2 ONguyễn Thanh Hải
51. Greenhouse Gases • Methane (CH4) is naturally present in the atmosphere from the decomposition of organic material • Anthropogenic sources – Production and transport of coal, natural gas, and oil – Decomposition of organic substances in municipal solid waste landfills, rice paddies – Raising of livestock • Huge quantities of methane are trapped in permafrostThS. Nguyễn Thanh Hải
52. Greenhouse Gases • Nitrous oxide (N2O) forms in tropical soils and is also released from the ocean • Anthropogenic sources – Agricultural fertilizers – Biomass burning – Industrial manufacturing (nylon, nitric acid) ThS. Nguyễn Thanh Hải
53. Greenhouse Gases • There are no natural sources of CFC’s, HCFC’s, or SF6 • Anthropogenic sources – Aerosols, foam manufacture, air conditioning and refrigeration – HCFC’s are much less damaging to the ozone layer, but equally or even more potent greenhouse gases ThS. Nguyễn Thanh Hải
54. Greenhouse Gases • The global warming potential (GWP) of a greenhouse gas depends on – its ability to absorb infrared light – its lifetime in the troposphere ThS. Nguyễn Thanh Hải
55. Greenhouse Gases • The main greenhouse gases have vastly different concentrations in the atmosphere ThS. Nguyễn Thanh Hải
56. Greenhouse Gases • The net effect for a greenhouse gas is found by multiplying its atmospheric concentration times its GWP ThS. Nguyễn Thanh Hải
57. Greenhouse Gas Feedback • One of the reasons greenhouse gases are predicted to have such a significant effect, even though they are present in small quantities, is because of the synergistic effect on water. • Increasing global temperature will raise the atmospheric concentration of H2O. Water vapor is the most important greenhouse gas. • Increasing water vapor will also cause more cloud formation, and the difficulty in estimating this effect is one of the major limitations on climate prediction models. ThS. Nguyễn Thanh Hải
58. CO2 and Temperature • There is a strong historical correlation between atmospheric CO2 concentration and temperatureThS. Nguyễn Thanh Hải
59. CO2 and Temperature • There has been a rapid rise in CO2 concentration since the industrial revolution, together with a large temperatureThS. Nguyễn Thanh Hải increase
60. Correlation Does Not Equal Causation • There is a theoretical reason why increasing atmospheric CO2 concentratio n should cause a temperatureThS. Nguyễn Thanh Hải rise
61. The Ozone Depletion - Global Warming Link • In general the public incorrectly links ozone depletion and global warming, often considering them the same thing. • Many of the HCFC replacements for CFC’s are much stronger infrared absorbers than either CO2 or • CFC’s.As these compounds replace the CFC’s, there is potential for new and important greenhouse ThS. Nguyễn Thanh Hải gases.
62. Is Ethanol a Better Fuel? • Burning ethanol does not cause a significant reduction in CO2 production CH3CH2OH (g) + 3O2 (g) 2CO2 (g) + 3H2O (l) C H (g) + 25/2O (g) 8CO (g) + 8 18 Hc =2 -1277 kJ 2 9H2O (l) • You have to burn more moles of ethanol Hc = -5116 kJ to get the same amount of energy as from gasoline ThS. Nguyễn Thanh Hải
63. Is Ethanol a Better Fuel? • Comparing the amount of carbon dioxide produced per unit of energy produced shows that ethanol and gasoline are virtually the same -3 C8H18 1.56 x 10 mol CO2/kJ -3 CH3CH2OH 1.57 x 10 mol CO2/kJ ThS. Nguyễn Thanh Hải
64. Is Ethanol a Better Fuel? ThS. Nguyễn Thanh Hải
65. Is Ethanol a Better Fuel? ThS. Nguyễn Thanh Hải
66. Is Ethanol a Better Fuel? ThS. Nguyễn Thanh Hải
67. Is Ethanol a Better Fuel? • The CO2 produced by burning the ethanol was just removed from the atmosphere by • However,photosynthesis enormous in the plant quantities of CO2 will also be produced by agricultural practice, transportation, production and ThS.distillation Nguyễn Thanh Hải of the
68. Is Ethanol a Better Fuel? • Ethanol production for fuel is about equal to the combustion of fossil fuels ThS. Nguyễn Thanh Hải