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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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The Oxygen Cycle

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h + N2 2N

h + N N + e-

h + O2 O2+ + e-

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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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Concentrations of Chlorine Monoxide and Ozone Versus Latitude

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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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Ozone Depletion (in purple) Over the South Pole

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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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Sources of CO2

(Increase all the time)

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The Carbon Cycle

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Yearly Variation of Carbon Dioxide Concentration at Mauna Loa, Hawaii.

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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

24Removing S from the fuel before combustion difficultRemove SO2 as it formed

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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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Typical Variations with Time in Concentration of Air Pollutants on a Smoggy Day.

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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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