Bài giảng Hóa học môi trường không khó - Nguyễn Thanh Hải

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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