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1
Chemistry in the AtmosphereChapter 17
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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The Nitrogen Cycle
Nitrogen Fixation: a process by which nitrogen is converted from its inert molecular form to a compound more readily available and useful to living organisms
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Atmospheric Nitrogen Fixation
2NO (g) + O2 (g) 2NO2 (g)
2NO2 (g) + H2O (g) HNO2 (aq) + HNO3 (aq)
Industrial Nitrogen Fixation
N2 (g) + 3H2 (g) 2NH3 (g)catalyst
N2 (g) + O2 (g) 2NO (g)electrical
energy
NH3 + 2O2 HNO3 + H2O
NH3 + HNO3 NH4NO3
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e-
p+
+ O O* + e-
O* O + h
+ N2 N2* + p+ + e-+
+N2* N2 + h+
green and red
blue and violet
O + NO NO2*
NO2* NO2 + h
Glowing tail section of space shuttleorange
Chemical Reactions in the Thermosphere
Solar Radiation
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Depletion of Ozone in the Stratosphere
UVO2 O + O
< 240 nm
O + O2 + M O3 + M
O3 production
O3 destruction
O3 O + O2
UV
O + O3 2O2
dynamic equilibrium
constant concentration of O3 in stratosphere
Inert substance like N(absorb some of the excess energy released)
Photodissociation of Oxygen
The production and destruction is in dynamic equilibriumOzone act as protective shield against UV radiation (absorbed the solar radiation in the range of 200-300nm)
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Effect of Chloroflorcarbon, CFC (Freon)
-Readily liquified
-Relatively inert
-Nontoxic
-Non-combustable
-Volatile
-Used as a coolants in refrigerators and air conditionars
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Depletion of Ozone in the Stratosphereeffect of Chloroflorcarbon, CFC (Freon)
O3 destruction
CFCl3 CFCl2 + ClUV (175-220nm)
CF2Cl2 CF2Cl + ClUV (175-220nm)
Cl + O3 ClO + O2
ClO + O Cl + O2+
O3 + O 2O2
Cl catalyzes the reaction
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Polar stratospheric clouds provide a surface for the reaction:
Cl2 + h 2ClSpring sunlight
HCl + ClONO2 Cl2 + HNO3
Cl + O3 ClO + O2
ClO + O Cl + O2+
O3 + O 2O2
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2H2S (g) + 3O2 (g) 2SO2 (g) + 2H2O (g)
SO2 (g) + OH (g) HOSO2 (g)
SO3 (g) + H2O (g) H2SO4 (g)
HOSO2 (g) + O2 (g) HO2 (g) + SO3 (g)
- Gasses: N2, CO2, HCl, HF, H2S, H2O
- Two third of the sulfur in the air comes from Volcanoes
-The hot H2S oxidized by air and some of the SO2 formed reduced by H2S to get S.
2H2O+SO2 3S + 2H2O
-The remaining SO2 react with water and form acid rains (see later)
-SO2 can reach the stratosphere and oxidized to SO3 which converted to H2SO4 gas. This aerosol destroy the stratosphere and cause a local cooling
(the H2SO4 could remain more than a year, absorbed solar radiation and hence drop the temperature near the volcanic irruption area)
Volcanoes
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The trapping of heat near Earth’s surface by gases in the atmosphere is the greenhouse effect.
H2O + h H2O*
CO2 + h CO2*
Greenhouse Effect.
-CO2 in air 0.033% by volume-It act like a glass in the greenhouses-If no CO2 the earth 30 degree cooler-CO2 and H2O allow the solar energy (mainly visible 400-700nm) to go to earth but absorbed (prevent) the earth heat (IR radiation 4000-25000 nm) to escape
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Why don’t N2 and O2 contribute to the greenhouse effect ?
N2 and O2 cannot absorb IR radiation.
Homonuclear (no change in the dipole moments, IR-inactive)
3 vibration modes of
H2O
2 of the vibration modes of CO2
H2O and CO2 can absorb IR radiation.
Polyatomic (change in the dipole moments, IR-active)
(IR-Inactive) (IR-active)
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The Change in Global Temperature from 1850 to Present.
Contribution to Global Warming by VariousGreenhouse Gases
Other gases also contribute to the global warming: CFCs, CH4, NOx and N2O
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Mean precipitation pH in 1994
SO2 (g) + OH (g) HOSO2 (g)
SO3 (g) + H2O (g) H2SO4 (g)
HOSO2 (g) + O2 (g) HO2 (g) + SO3 (g)
Acid Rain
Damage the stone (corrosion of stones) and also toxic to vegetation
-CO2 + rain water not expected to lower the pH less than 5.5-SO2 and Nitrogen oxides is responsible for the high acidity
From volcanic eruption
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CaCO3 (s) + H2SO4 (aq) CaSO4 (s) + H2O (l) + CO2 (g)
2CaCO3 (s) + 2SO2 (g) + O2 (g) 2CaSO4 (s) + CO2 (g)
The Effect of Acid Rain on the Marble Statue of George Washington (New York, City). Photos Taken in 1944 and 1994
Limestone and marble
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Photochemical smog is formed by the reactions of automobile exhaust in the presence of sunlight.
Primary pollutants: NO, CO and unburned hydrocarbons
Secondary pollutants: NO2 and O3
N2 (g) + O2 (g) 2NO (g)
2NO (g) + O2 (g) 2NO2 (g)
NO2 (g) + h NO (g) + O (g)
O (g) + O2 (g) + M O3 (g) + M
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U23892
4.51 x 109 yrTh234
9024.1 days
Pa23491
1.17 minU234
922.47 x 105 yr
Th23090
7.5 x 104 yrRa226
881.6 x 103 yr
Rn22286
3.82 dPo218
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