1 Chemistry in the Atmosphere Chapter 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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3 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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5 Atmospheric Nitrogen Fixation 2NO (g) + O 2 (g) 2NO 2 (g) 2NO 2 (g) + H 2 O (g) HNO 2 (aq) + HNO 3 (aq) Industrial Nitrogen Fixation N 2 (g) + 3H 2 (g) 2NH 3 (g) catalyst N 2 (g) + O 2 (g) 2NO (g) electrical energy NH 3 + 2O 2 HNO 3 + H 2 O NH 3 + HNO 3 NH 4 NO 3

6 The Oxygen Cycle

7 h + N 2 2N h + N N + e - h + O 2 O e -

8 e-e- p+p+ + O O * + e - O * O + h + N 2 N 2 * + p + + e N 2 * N 2 + h + green and red blue and violet O + NO NO 2 * NO 2 * NO 2 + h Glowing tail section of space shuttle orange Chemical Reactions in the Thermosphere Solar Radiation

9 Depletion of Ozone in the Stratosphere UV O 2 O + O < 240 nm O + O 2 + M O 3 + M O 3 production O 3 destruction O 3 O + O 2 UV O + O 3 2O 2 dynamic equilibrium constant concentration of O 3 in stratosphere Inert substance like N (absorb some of the excess energy released) Photodissociation of Oxygen The production and destruction is in dynamic equilibrium Ozone act as protective shield against UV radiation (absorbed the solar radiation in the range of nm)

10 Effect of Chloroflorcarbon, CFC (Freon) -Readily liquified -Relatively inert -Nontoxic -Non-combustable -Volatile -Used as a coolants in refrigerators and air conditionars

11 Depletion of Ozone in the Stratosphere effect of Chloroflorcarbon, CFC (Freon) O 3 destruction CFCl 3 CFCl 2 + Cl UV ( nm) CF 2 Cl 2 CF 2 Cl + Cl UV ( nm) Cl + O 3 ClO + O 2 ClO + O Cl + O 2 + O 3 + O 2O 2 Cl catalyzes the reaction

12 Concentrations of Chlorine Monoxide and Ozone Versus Latitude

13 Polar stratospheric clouds provide a surface for the reaction: Cl 2 + h 2Cl Spring sunlight HCl + ClONO 2 Cl 2 + HNO 3 Cl + O 3 ClO + O 2 ClO + O Cl + O 2 + O 3 + O 2O 2

14 Ozone Depletion (in purple) Over the South Pole

15 2H 2 S (g) + 3O 2 (g) 2SO 2 (g) + 2H 2 O (g) SO 2 (g) + OH (g) HOSO 2 (g) SO 3 (g) + H 2 O (g) H 2 SO 4 (g) HOSO 2 (g) + O 2 (g) HO 2 (g) + SO 3 (g) - Gasses: N 2, CO 2, HCl, HF, H 2 S, H 2 O - Two third of the sulfur in the air comes from Volcanoes -The hot H 2 S oxidized by air and some of the SO 2 formed reduced by H 2 S to get S. 2H 2 O+SO 2 3S + 2H 2 O -The remaining SO 2 react with water and form acid rains (see later) -SO 2 can reach the stratosphere and oxidized to SO 3 which converted to H 2 SO 4 gas. This aerosol destroy the stratosphere and cause a local cooling (the H 2 SO 4 could remain more than a year, absorbed solar radiation and hence drop the temperature near the volcanic irruption area) Volcanoes

16 The trapping of heat near Earth’s surface by gases in the atmosphere is the greenhouse effect. H 2 O + h H 2 O * CO 2 + h CO 2 * Greenhouse Effect. -CO 2 in air 0.033% by volume -It act like a glass in the greenhouses -If no CO 2 the earth 30 degree cooler -CO 2 and H 2 O allow the solar energy (mainly visible nm) to go to earth but absorbed (prevent) the earth heat (IR radiation nm) to escape

17 Why don’t N 2 and O 2 contribute to the greenhouse effect ? N 2 and O 2 cannot absorb IR radiation. Homonuclear (no change in the dipole moments, IR-inactive) 3 vibration modes of H 2 O 2 of the vibration modes of CO 2 H 2 O and CO 2 can absorb IR radiation. Polyatomic (change in the dipole moments, IR- active) (IR-Inactive)(IR-active)

18 Sources of CO 2 (Increase all the time)

19 The Carbon Cycle

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

21 The Change in Global Temperature from 1850 to Present. Contribution to Global Warming by Various Greenhouse Gases Other gases also contribute to the global warming: CFCs, CH 4, NO x and N 2 O

22 Mean precipitation pH in 1994 SO 2 (g) + OH (g) HOSO 2 (g) SO 3 (g) + H 2 O (g) H 2 SO 4 (g) HOSO 2 (g) + O 2 (g) HO 2 (g) + SO 3 (g) Acid Rain Damage the stone (corrosion of stones) and also toxic to vegetation -CO 2 + rain water not expected to lower the pH less than 5.5 -SO 2 and Nitrogen oxides is responsible for the high acidity From volcanic eruption

23 CaCO 3 (s) + H 2 SO 4 (aq) CaSO 4 (s) + H 2 O (l) + CO 2 (g) 2CaCO 3 (s) + 2SO 2 (g) + O 2 (g) 2CaSO 4 (s) + CO 2 (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

24 Removing S from the fuel before combustion difficult Remove SO 2 as it formed

25 Photochemical smog is formed by the reactions of automobile exhaust in the presence of sunlight. Primary pollutants: NO, CO and unburned hydrocarbons Secondary pollutants: NO 2 and O 3 N 2 (g) + O 2 (g) 2NO (g) 2NO (g) + O 2 (g) 2NO 2 (g) NO 2 (g) + h NO (g) + O (g) O (g) + O 2 (g) + M O 3 (g) + M

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

27 U x 10 9 yr Th days Pa min U x 10 5 yr Th x 10 4 yr Ra x 10 3 yr Rn d Po

28 Home Radon Detectors