Lecture 25 Atmosphere environment Read HW BLB 18 1 4 BLB 18 9 11 15 29 69 Sup 18 1 3 Know ozone chemistry chemistry of the lower atmosphere sulfer compounds acid rain nitrogen oxides smog check out the environmental climate change folder under Lessons on our Angel site for more links movies fyi only Need help Get help TAs in CRC 211 Whitmore and SI hours on Chem 110 website my office hours Mon 12 30 2 Tues 10 30 12 in 324 Chem Bldg or 326 Chem Bonus deadline for BST 8 Intermolecular forces March 26 Bonus deadline for BST 9 Solutions dilutions April 2 Exam 3 Monday April 6 6 30 Sheets Page 1 Lecture 25 Pressure altitude atmospheric gases 78 N2 21 O2 some Ar CO2 other gases pressure at a given altitude depends upon weight of gas above it pressure decreases exponentially as altitude altitude km 0 50 100 200 Sheets P atm 1 10 3 10 6 10 13 Page 2 collision frequency s 1 1010 107 103 1 Lecture 25 Composition of the atmosphere mole fraction Xa N2 O2 represent 99 of atmosphere ppm parts per million ppm example neon 106 XNe 0 00001818 Ne concentration 18 18 ppm see BLB Table 18 1 if you know barometric pressure you can determine partial pressure of the gas recall those partial pressures Example What is the partial pressure of neon if the barametric pressure is 0 987 atm PNe Sheets Page 3 Lecture 25 Atmospheric layers based on temperature profile troposphere T as altitude where we live weather planes stratosphere T warming caused by ozone cycle UV light absorbed mesosphere T low density of gases thermosphere T high energy radiation is absorbed ions formed present life could NOT survive above ground if all solar radiation reached Earth recall pressure profile of atmosphere low pressure molecular collisions thus chemical reactions occur frequently temperature profile of atmosphere average KE of molecules is high Sheets Page 4 T means Lecture 25 Photochemistry in the atmosphere photoexcitation electronic excitation Chap 6 h NO2 NO2 excited state photodissociation bond broken by absorption of a photon h O2 O O bond E O2 495 kJ mol need sufficient energy 242 nm verify this for yourself recall E h c Chap 6 O2 and O concentrations vary with altitude photoionization removal of a valence e from a molecule by absorption of a photon h N2 N2 e need energy the ionization potential 1495 kJ mol 80 1 nm Sheets Page 5 Lecture 25 Solar radiation penetration in the atmosphere higher energy lower energy 100nm 170 300nm 330nm thermosphere NO photoO2 ionization O e mesophere NO O2 stratosphere photodissociation O2 O NO O3 troposphere photoexcitation O2 N2 earth Sheets Page 6 Lecture 25 Ozone O O O O O O resonance MG VSEPR bond length 1 28 O2 is 1 21 light blue gas BP 111 3 C pungent odor electrical discharges Hf 142 3 kJ mol reactive less stable than O2 see Lecture 39 in troposphere O3 is an irritant see smog in stratosphere O3 is essential peak of O3 is at 25 km O3 10 ppm 350 nm UV induces photochemistry in many organic molecules skin cancer ozone in stratosphere with 240 320 nm Sheets Page 7 most radiation Lecture 25 The natural ozone cycle formation of O3 O2 h 2O O O2 O3 UV blocking by O3 O3 h O2 O 242 nm 320 nm the small amount of O3 in stratosphere reflects the delicate balance between creation destruction http www theozonehole com Sheets Page 8 Lecture 25 Chlorofluorocarbons CFCs examples CFCl3 freon 11 properties relatively inert easily liquified non combustible volatile CF2Cl2 freon 12 uses aerosol propellants refrig coolants cleaning solvents polymer mfg BUT CFC destroys ozone CF2Cl2 h CF2Cl Cl 240 nm 2Cl 2O3 2ClO 2O2 ClO ClO ClOOCl ClOOCl h ClOO Cl ClOO h Cl O2 NET 2O3 3O2 Cl atom from CFC catalyzes O3 destruction speeds up reaction but is not consumed or used up during the reaction 1 Cl atom destroys 100 000 O3 molecules Sheets Page 9 Lecture 25 Ozone hole see BLB Fig 18 5 special conditions at the South Pole create dramatic seasonal loss of ozone complex reactions related to presence of polar stratospheric clouds explain the seasonal nature of the loss nearly complete loss of ozone at some altitudes near the poles and 50 total reduction at other latitudes near the poles away from the poles depletion is not as great and is seasonal global O3 concentration has declined since 1980 you can burn in 7 min in Chile Argentina Australia 6 lethal skin cancer vs 0 3 general world population bring your sunblock Sheets Page 10 Lecture 25 Ozone hole cont http www atm ch cam ac uk tour part2 html http www nasa gov vision earth environment ozone resource page html Ozone hole on 7 Oct 2008 Sheets Page 11 Lecture 25 Ozone hole cont the good news 1987 Montreal Protocol called for virtual elimination of ozone depleting substances signed by 160 nations 1996 production and use of CFCs banned worldwide recovery by 2100 See http video google com videoplay docid 8206266264728754527 q ozone hole total 212 start 0 num 10 so 0 type search plindex 0 the bad news CFCs are stable will remain in troposphere and continue to diffuse up to stratosphere if CFC production or release into the atmosphere DID stop ozone depletion would continue for at least several decades effects include 2 10 increase in skin cancers per 1 decrease in ozone possible effects on crop yields and EPA estimates that ozone levels will return to normal by 2050 if full compliance with protocol is achieved Sheets Page 12 Lecture 25 Our effect on the troposphere greenhouse gases global warming acid rain photochemical smog Sheets Page 13 Lecture 25 Greenhouse gases global warming http www al noaa gov W WWHD pubdocs mission html Earth emits IR radiation some of which is trapped or by greenhouse gases the good keeps Earth s temperature 15 C 59 F instead of 18 C 0 F evens out day night temperature variation http www markstivers com cartoons Stivers 206 1002 20Bush 20and 20global 20warming gif Swimwear www funnyhub com pictures pages global warming swimwear html Sheets Page 14 Lecture 25 http www gcrio org ocp96 figs fig20 gif http atschool eduweb co uk kingworc departments geography nottingham atmosphere pages gfx greenhouseeffect gif Sheets Page 15 Lecture 25 Greenhouse gases global warming cont the bad greenhouse gas levels keep increasing so global temperature keeps increasing CO2 fossil fuel biomass combustion volcanic eruptions but plants help take up excess CO2 CH4 animal gas stinky swamp natural gas venting incomplete combustion www carbuyersnotebook com archives Cow jpg coal mining H2O vapor evaporation condensation http en wikipedia org wiki Image Global
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