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HÓA HỌC MÔI TRƯỜNG KHÔNG KHÍ GV: ThS. NGUYỄN THANH HẢI Bài giảng cho lớp MT K30 ThS. Nguyễn Thanh Hải TẦNG OZONE ThS. Nguyễn Thanh Hải TẦNG OZONE ThS. Nguyễn Thanh Hải TẦNG OZONE ThS. Nguyễn Thanh Hải Cơ chế tạo thành ozone O2 + hn  2O Sự phân hủy ozone tự nhiên O3 + hn  O + O2 O3 + O  2O2 2O3 + hn  3O2 O2 + O + M  O3 + M O2 + O + M  O3 + M 3O2 +hn  2O3 ThS. Nguyễn Thanh Hải Các tia UV • UVA: 320 – 400 nm • UVB: 290 – 320 nm • UVC: <290 nm ThS. Nguyễn Thanh Hải TẦNG OZONE ThS. Nguyễn Thanh Hải 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 ThS. Nguyễn Thanh Hải ThS. Nguyễn Thanh Hải Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải Phổ hấp thu của DNA Tia UV làm các phân tử DNA tham gia các phản ứng quang hóa ThS. Nguyễn Thanh Hải Phổ hấp thu của DNA ThS. Nguyễn Thanh Hải ThS. Nguyễn Thanh Hải TẦNG OZONE • Hydroxyl ( . OH) . OH + O3 = HO2 . + O2 HO2 . + O = . OH + O2 O + O3 = 2 O2 • Chlorine và bromine (Cl và Br) Cl . + O3 = ClO . + O2 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 TẦNG OZONE ThS. Nguyễn Thanh Hải • Vùng UV-B mở rộng tới vùng UV-C khiến ozone không thể loại bỏ hết các tia UV Ảnh hưởng của sự suy giảm ozone ThS. Nguyễn Thanh Hải • The UV-B region will expand as there will be insufficient ozone to remove all the UV light Effect of Ozone Depletion • Currently, one in five Americans will develop skin cancer in their lifetime Basal cell carcinoma • 1-2% increase in skin cancer for each 1% decrease in ozone ThS. Nguyễn Thanh Hải • Naturally, ozone is continually formed and destroyed by light Causes of Ozone Depletion Formation 3O2 +hn  2O3 Removal 2O3 + hn  3O2 • This results in steady state concentration of ozone in the stratosphere • There are minor depletion reactions caused by other stratospheric gases including water vapor, nitrogen oxides, methane, and methyl bromide (produced ThS. Nguyễn Thanh Hải • Human activity increases the amount of naturally occurring methane and nitrogen oxides in the stratosphere Anthropogenic Ozone Depletion • The major causes are photochemical decomposition of chlorinated and brominated hydrocarbons CFCl3 (CFC-11) ThS. Nguyễn Thanh Hải Anthropogenic Ozone Depletion • Ultraviolet light causes photochemical breakdown, releasing Cl or Br free radicals ThS. Nguyễn Thanh Hải Anthropogenic Ozone Depletion • The mechanism of the reaction is a typical free radical reaction  CFCl3 + hnCFCl2· + 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 molecules  ClO· + ·O O2 + Cl·  Cl· + O3 ClO· + O2 ThS. Nguyễn Thanh Hải Anthropogenic Ozone Depletion • The ultimate fate of the Cl atom may be to react with CH4 Cl· + CH4 CH3· + HCl • The CFCl2· probably continues to be photolysed to produce more free chlorine CFCl2· + hnCFCl + Cl· • HCl eventually washes out into the troposphere, but it acts as a reservoir of Cl atoms that is the cause of the polar ozone holes ThS. Nguyễn Thanh Hải 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 chlorine carriers (HCl and ClONO ) ThS. Nguyễn Thanh Hải 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 very long time CFC-11 Trichlorofluoromethane (45 years) CFC-115 Monochloropentafluoroethane (1700 years) • Adding hydrogen to the molecule dramatically speeds up its decomposition in the troposphereHCFC-21 Dichlorofluoromethane (2 years) ThS. Nguyễn Thanh Hải The Montreal Protocol • Originally ratified in 1987, it has been amended 5 times (1990, 1992, 1995, 1997, 1999) Only 12 countries have not ratified this treaty •Equatorial Guinea •Eritrea •Guinea-Bissau •Afghanistan •Bhutan •Cook Islands •Iraq •Niue •East Timor •Andorra •Holy See •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 medical inhalers until 2005) ThS. Nguyễn Thanh Hải 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 by developed nations ThS. Nguyễn Thanh Hải The Canadian Picture  We have dramatically reduced our consumption of ozone depleting substances. ThS. Nguyễn Thanh Hải The Future • Although no longer allowed, there are still large amounts of CFC’s in already produced goods. ThS. Nguyễn Thanh Hải 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 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 works by ThS. Nguyễn Thanh Hải Historical Background • Joseph Fourier (1768–1830) studied the role of solar radiation• John Tyndall (1820– 1886) in 1859 emphasized the role of water vapor • Svante Arrhenius (1859 - 1927) emphasized the role played by carbon dioxide ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • The sun is a blackbody radiator with a temperature of about 5700 K ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • Gases in the earth’s atmosphere absorb energy where they have allowed quantum transitions ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • Gases in the earth’s atmosphere absorb energy where they have allowed quantum transitions ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • Direct absorption of solar radiation contributes very little to atmospheric heating ThS. Nguyễn Thanh Hải • There is a steady state between the amount of solar radiation the earth receives, and what it re- radiates back into space How the Greenhouse Effect Actually Works ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • About 70% of the sun’s irradiation reaches the earth’s surface (surface albedo) ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • About 70% of the sun’s irradiation reaches the earth’s surface (surface albedo)• The average temperature of the earth is about 15 ºC (288 K) ThS. Nguyễn Thanh Hải 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 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 How the Greenhouse Effect Actually Works • A much smaller amount of the earth’s radiant energy is absorbed by CO2 ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • CO2 is important as it absorbs strongly in a region where water does not ThS. Nguyễn Thanh Hải How the Greenhouse Effect Actually Works • Other gases also contribute to make up the total absorption spectrum of the earth’s atmosphere There is a large tmospheric window in the v sibl , and a much smaller one in the infrared ThS. Nguyễn Thanh Hải 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 How the Greenhouse Effect Actually Works • A 235 W/m2 radiating black body would have a temperature of - 18 ºC• Since the earth’s actual average temperature is about 15 ºC, the greenhouse effect contributes approximately 33 º ThS. Nguyễn Thanh Hải Greenhouse Gases • Water vapor is by far the most important greenhouse gas ThS. Nguyễn Thanh Hải 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 H2O ThS. Nguyễn Thanh Hải 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 • Huge quantities of methane are trapped in permafrost – Decomposition of organic substances in municipal solid waste landfills, rice paddies – Raising of livestock ThS. Nguyễn Thanh Hải 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 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 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 Greenhouse Gases • The main greenhouse gases have vastly different concentrations in the atmosphere ThS. Nguyễn Thanh Hải Greenhouse Gases • The net effect for a greenhouse gas is found by multiplying its atmospheric concentration times its GWP ThS. Nguyễn Thanh Hải 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 CO2 and Temperature • There is a strong historical correlation between atmospheric CO2 concentration and temperature ThS. Nguyễn Thanh Hải CO2 and Temperature • There has been a rapid rise in CO2 concentration since the industrial revolution, together with a large temperature increase ThS. Nguyễn Thanh Hải Correlation Does Not Equal Causation • There is a theoretical reason why increasing atmospheric CO2 concentratio n should cause a temperature rise ThS. Nguyễn Thanh Hải 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 gases. ThS. Nguyễn Thanh Hải Is Ethanol a Better Fuel? • Burning ethanol does not cause a significant reduction in CO2 production CH3CH2OH (g) + 3O2 (g)  2CO2 (g) + 3H2O (l) Hc = -1277 kJC8H18 (g) + 25/2O2 (g)  8CO2 (g) + 9H2O (l) Hc = -5116 kJ• You have to burn more moles of ethanol to get the same amount of energy as from gasoline ThS. Nguyễn Thanh Hải 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 C8H18 1.56 x 10 -3 mol CO2/kJ CH3CH2OH 1.57 x 10 -3 mol CO2/kJ ThS. Nguyễn Thanh Hải Is Ethanol a Better Fuel? ThS. Nguyễn Thanh Hải Is Ethanol a Better Fuel? ThS. Nguyễn Thanh Hải Is Ethanol a Better Fuel? ThS. Nguyễn Thanh Hải Is Ethanol a Better Fuel? • The CO2 produced by burning the ethanol was just removed from the atmosphere by photosynthesis in the plant • However, enormous quantities of CO2 will also be produced by agricultural practice, transportation, production and distillation of the ThS. Nguyễn Thanh Hải Is Ethanol a Better Fuel? • Ethanol production for fuel is about equal to the combustion of fossil fuels