Bài giảng Hóa học môi trường không khí

HÓA HỌC MÔI TRƯỜNG
 KHÔNG KHÍ
 GV: ThS. NGUYỄN THANH HẢI
 Bài giảng cho lớp MT K30
 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
 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
 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 = 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
 TẦNG OZONE
ThS. Nguyễn Thanh Hải
 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
 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
 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 
 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
 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·
  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
 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
 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 ) 
 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
 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)
 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
 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 
ThS. Nguyễnworks Thanh Hải by 
 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
 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 
 quantumThS. Nguyễn Thanh Hải
 transitions
 How the Greenhouse Effect 
 Actually Works
• Gases in the 
 earth’s 
 atmosphere 
 absorb 
 energy 
 where they 
 have 
 allowed 
 quantumThS. Nguyễn Thanh Hải
 transitions
 How the Greenhouse Effect 
 Actually Works
• Direct 
 absorption 
 of solar 
 radiation 
 contributes 
 very little to 
 atmospheric 
 heating
 ThS. Nguyễn Thanh Hải
 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
 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 
• The(surface average albedo) 
 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
• 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
 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 -
• 18Since ºC the earth’s 
 actual average 
 temperature is 
 about 15 ºC, the 
 greenhouse effect 
 contributes 
 ThS. Nguyễn Thanh Hải
 approximately 33 º 
 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 
 ThS.H2 ONguyễn 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
 – 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
 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 
 temperatureThS. Nguyễn Thanh Hải
 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
 Correlation Does Not Equal 
 Causation
• There is a 
 theoretical 
 reason why 
 increasing 
 atmospheric 
 CO2
 concentratio
 n should 
 cause a 
 temperatureThS. Nguyễn Thanh Hải 
 rise
 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.
 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
 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
 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 
• 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 
 Is Ethanol a Better Fuel?
• Ethanol production for fuel is about equal 
 to the combustion of fossil fuels
 ThS. Nguyễn Thanh Hải