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by: Guiseppe Bednar


Guiseppe Bednar

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Class Notes
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This 14 page Class Notes was uploaded by Guiseppe Bednar on Friday October 30, 2015. The Class Notes belongs to CHEM 5151 at University of Colorado at Boulder taught by Staff in Fall. Since its upload, it has received 18 views. For similar materials see /class/232188/chem-5151-university-of-colorado-at-boulder in Chemistry at University of Colorado at Boulder.




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Date Created: 10/30/15
Lecture 22 Atmospheric Chemistry and Climate Reguired Reading FP Chapter 14 only sections that cover Suggested Introductory Reading Jacob Chapter 7 Atmospheric Chemistry CHEM5151 ATOC5151 Spring 2005 Prof JoseLuis Jimenez Introduction Climate longterm statistical average of weather Lecture Outline A Radiation balance as driver for climate B Greenhouse gases C Aerosols Caveats Once more one could teach an entire course on this topic so we will only cover the main points There is a lot more to Climate Change than atmospheric chemistry Atmospheric circulation dynamics ocean circulation and chemistry prec1p1tat10n sea level reglonal d1fferences But changes in atmospheric chemistry are the driver of CC IPCC Report To learn more see IPCC report 7 AR third assessment report 7 vailable online for free httpwwwgridanoclimateipccitarwgl Link on class page The bible ofclimale cl unge 7 It39s big an thick 7 It ms written by a committee 7 It deals with cataclysmic events such as oods and droughts 7 No one reads it from cover to cover Climate Change 2001 0 an openith on any page and find something interesting 7Itisfull t39 39 439 39 7 It has its true believers and its rabid skeptics from Steve Schwartz DOE Brunk aven Nat Lab Another report FAR coming in 72007 Is Climate Change Happening IPCC 1995 SAR 7 The balance of evidence suggests a discernible human in uence on global climatequot IPCC 2001 TAR 7 In the light of new evidence and taking into account the remaining uncertainties most of the observed Warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrationsquot Pieter Tans N OAA 7 with CO2 increasing by 50 since preindustrial times I can t see how someone could think that climate Would not have changedquot Even the Bush administration agrees that CC is happening Real question is the magnitude and region temp patterns Radiative Balance of the Earth 1 Solar radiation ux Terrestrial 1 Ilsk radiation flux I 0T5 SUN Sun is close to blackbody at 5800K 39 Power emitted by blackbody E 0T4 ais StefanBoltzmann constant 567 X 10398 W m392 K394 Sun emits 64 MW m392 Total power emitted by sun Es 47st2 GT4 E 4 X 1026 W Distributed uniformly in all directions Radiative Balance of the Earth 11 ES 472R 0TS4 0714R 0 Power density at any distance from the sun FS 4M2 W d2 RS 7 x 105 km d 15x 108km IFS 1397 W m2 actually 1368 Substituting we get 0 That is power in Earth s plane o On avera e the ower 39 2 g p FS FS EREZ 342 Wm z 472RE 4 over the Earth s surface Radiative Balance of the Earth 111 I Simplest case no atmosphere complete absorption 7 In thermal equilibrium Earth F E 039ng 342 Wm z would reradiate same amount AE0FFE I Life is not so simple39 TE 279K Observed 288K 7 Albedo 31 from satellites I chtion ofincoming solar radiation F s FSH39A 235 W quot1 2 re ected back to space I 107 W m Z isjust re ected FE UTE 235 Wm2 I So real emission from Earth is smaller 342 7107 235 W m39Z TE 254 K way 00 cald I Reality 7 Atmosphere absorbs radiation 7 254 K is effective T of Earth Atmosphere system T 55 km The Real Radiative Balance of the Earth Solar Radiation Longwave Radiation W Re ected Soiar Incomlng 235 Outgoing Radiation 3A2 Solar Longwave 107 Wrrr2 Radiation Radialion 2 wirra 235 Wrrr2 Reflected by Clouds Aerosoi and f 40 Atmosphere Emittea by Atmospheric Atmosphere 165 Window Greenhouse Absorbed by 67 Almosphere 63595 324 3 Back Radiation ago 53 24 7s Suriaoe Absorbed by Suriace Thermals Evapo Radiation 324 transpiration Absorbed by Suriie39e From IPCC 2001 i Earth s Surface is not Uniform o More absorption at tropics 400 o More emission at 350 oles N 300 p 250 o On average AE O at E 200 Emitted outgoing 39 quot h each locatlon g 150 4 39 quotgwa ee g I 100 Eshort Elong Erransport O o 50 Absorbed incoming short wavelength O llllllllllllllll Is What drlves the 80 60 4O 20 0 20 40 60 80 Lamude large scale FIGURE 145 Annual mean radiation measured by satellite in 39 1988 at the top of the atmosphere as a function of latitude for atmospherlc incoming absorbed shortwavelength radiation and emitted outgoing Circulation longwavelength radiation adapted from Trenberth and Solomon 1994 Hadley etc Wavelength Dependence SUN EARTH 5800K 290K 1 Inermalizedl I t WAVELENGTH um I lllllllll lllllllll 1 Ill 039 D 2 D 5 i 2 5 10 15 20 30 t 130 8 Figure 711 Efficiency of absorption of radiation by the atmosphere as a function of wavelength Major absorbers are identified 0 Transparent in Visible and atmospheric window Also eg 4 mm but we don t care Saturation of Absorption at a Certain A Weak absorption 05 C httpWWW orc soton ac uk stphys1004lectures04 lecture205202004 pdf Beer s Law absorption Stronger a x C 71 1 mm 139 Saturated alog C C is gas concentration E C Weak C absorber Gian quot t 1 E I I I l I I 0 xs 0 xS xv vo FIGURE 148 a Meaning of equivalent width W b Doppler and Lorentzian lineshapes for equivalent halfwidths c trans mission curves for an absorption line for a weak and strong absorber respectively adapted from Lenoble 1993 From FPampP Potential Greenhouse Gases 104 Four condltlons for a greenhouse gas to be arc14 CHF 3 important CFC 33313 CFC13 CFC 11 Stron absor tion cross CFC12 CFC CC4 g p E E 103 C 416 CHze CHCI3 sectlon g 9 2302 CFC12 CFC11 quot HNO CFC22 Large enough concentratlor 55 3 3 02114 CHQCIZ H PAN H 0 PAN o3 Long hfetlme CH4 2N CFC22 Absorb in the atmospheric g 35 CF02 CHCI3 CHaCGIa CFC 13 0 IE 102 CHZCI2 so w1ndow lt g ECZHZ 2 H20 60 co2 26 03 CZHS 8 ocs quotCHSCCIB Enhanced greenhouse 101 CF I effect 7 a 9 10 11 12 13 coz N20 CH4 o3 CFCs Wm HCFCS SF6 FIGURE 1410 Intrinsic infrared absorption band strengths of Ramanathan 1988a 1988b some potential greenhouse gases in the atmospheric window from From FPampP I me Stzve 5mm DOE Imp wawzcdbl l guvstzveAzmsolslkchmtzchmg pdl39 Summary of GHG Forcings The global mean radiative forcing ol the cltmale system lor the year 2000 relative to l 50 Hllncamans N20 CH4 coz Yroposphsrlc ems 11 Slratosphouc adtallve mmng lWatIs Der square metre High Medium Medmm Level or Sclnnhltc Underslandlng A mm Summary for Policymakers lutetutvunm y H m on lemle mum Radiative Forcing F F change in radiation tropopause due to increase in a greenhouse gas 7 Use the tropopause because surface troposphere are tightly coupled by convection and mixing 7 Tropospheric absorption leads to stratospheric cooling less radiation to absorb Climate change per unit RF 7 Use average surface T as proxy for climate AT 1 F 7 1 climate sensitivity K Wm39z 7 Black body at 255 K 027 K Wm39z 7 Range of estimates from models 0311 K Wm39z The Earth s Climate Sensitivity 0 What is Earth 339 climate sensitivity National Academy Report 39Charney 1979 3 We estimate the most probable global wai iiiing for a doubling ot COj to be near 3 degrees C with a probable error ol39plns 0139 minus 15 degrees Intergovernmental Panel on Climate Change IPCC 2001 Climate sensitivity to C0 doubling is likely to be in the range 15 to 45T This level of nnccrminir is not very useful for policy planning From Steve Schwartz DOE httpWWW ecd bnl govsteveAerosolsampClimateChange pdf CO2 Atmospheric Increase 1958 on 360 350 E g 340 639 O 330 320 310llllllllllllllllllllllllllllllllllllll 1958 62 66 7O 74 78 82 86 90 1994 Year FIGURE 1412 Measured CO2 concentrations at Mauna Loa Hawaii from 1958 to 1994 The line represents the atmospheric CO2 expected if 559 of the cumulative emissions of CO2 from fossil fuel combustion and cement production remained in the atmosphere F FPampP adapted from Keeling et al 1995 0 NC Atmospheric Increase last 40000 years 320 E 280 E v 240 c5 0 200 F39 I J I I l I l 5 1O 15 20 25 30 35 40 Age kilo years BP FIGURE 1413 Concentrations of atmospheric C02 measured using gases trapped in ice cores from Byrd Station Antarctica from 5000 to 40000 years before the present bp adapted from Anklin et al 1997 From FPampP T Global net primar 39 production Changing Atmosphere yC e l and respiration land use m m 0 Very large uxes 60 613 16 05 between ci il li n and atmosphere and pmgggn 92 soils oceans Sog avf m 2790 Oceans are the W ma or reservon Mariam 3 From ac1d ram a lecture Henry s m 1 0 4 law HCO339 4 i co 2 raid 3 Intermediate camquot Lowenng ocean 3559 7 pH 38100 02 Limited by ocean From FPampP m1X1ng gt long 39 FIGURE 1411 Summary of global carbon cycle Amount in gigarons of C 10 metric tons 10395 of C Reservoirs are shown in arentheses and uxes gigatons of C per year are E P indicated by arrows Note that the time scales associated with the various processes vary adapted rum IPCC 1996 Trop Warming vs Strat Cooling co2 Traps radiation in the lower 50 troposphere Radiates more E 4039 effectively in the f 30 39 upper atmosphere 5 amp Stratospherlc 20 cooling has been 1O observed Mostly due to n I lower strat O 3925 3920 15 10 05 00 3 AT C Effects on FIGURE 147 M d 1 39 L J A l a r dynamlcsa 03 Changes as a function of altitude due to an increase in CO2 from 315 absorption ppm in 1960 to 370 ppm projected for 2000 no feedbacks taken into From FPampP account adapted from Rind and Lacis 1993 Atmospheric concentration 20 mph Increase of Other Constituents I l 350 Carbon Dioxide 1395 340 1 0 320 300 05 280 We V Warmammng 00 7 r 397 17503 Melhane 0 5 15001 04 03 1250 02 1000 01 750 F 35quot AMMH no t 310i Nitrous Oxide 39 03915 if 1 010 i P 290 3 3 005 39 reZJ39 39 270 2 39 39 439 00 250 t I V 1000 1200 1 400 1600 1800 2000 Year Radiative forcing Wm 2 Not just CO2 but also CH4 and N20 have increased rapidly 0 Also S from sulfate aerosols More later b1 i 200 Sulphur Sulphate concentration mg 3042 per tonne of ice 8 o From IPCC 2001 10 CH4 increase and budget TABLE 141 Estimated Methane Sources during the Mid 19805 issions Source Tg of C year Natural 260 i 30 Anthropogenic 370 i 40 Gas leakage and oil production 85105 Coal mining 2545 18 Rlce elds 20450 Rummarlts 65 100 A Biomass burning 2060 g Animal wastes 20740 g 17 r Sanitary land lls 20750 v s R I From Crutzen 1995 o s ng ofC 10 gofC 16 W N a 15 Ween FIGURE 1416 Averaged 3D methane concentrations in the marine boundary layer Lines are guides for the eye adapted from Dlugokencky at 11 1994a Summary of GHGs and Aerosols Ta The global mean radiative forcing of the climate system a for the year 2000 relative to 1750 E 6 3 2 S E 6 A Halocarbons j 2 2 N20 Aerosols o E m CH g E 4 Black it a go 0 carbon from E 3 l 39 2 Tropospheric will Mineral E burning USI ii m rh Ci 3 1 D e e L 1 5 Stratospheric Organic E 5 5 Ozone I quot Biomass E 2 1 To Ae sol lt w Sulphate loss burning ind Bot e E IueI of Cl D g burning 0 rd Q a 2 EA E g High Medium Medium Low Very Very Very Very 3 Low Low Low Low gt in 2 Level of Scienti c Understanding 0 LE Repait 01 v u39rlxlrlr Group i v vl tlile LEVPlrll l39lFH39IlEil Partial rm CliillxgiPllgEli l ig 11 Aerosol Effects Physical basis already covered in lecture 20 Very uncertain because of 7 Short lifetime 7 Very incomplete data 7 Great complexity of sizes amp compositions Direct effect 7 Aerosols scatter sunlight back to space gt cooling Black carbon absorbs gt warming 7 Most efficient when d N i submicron aerosols 7 Same physics that cause visibility degradation 7 All aerosol constituents participate in scattering If they absorb water they scatter more me Sim saime non h pllwww cdbnlgovslzvzlAzmsolsichmmclmig par Aerosol Variability Delermined by sunplmlmueu y Nonh central Oklahoma 7 Daily average al 510nm 020 025 Aerosol optical depth 0 15 o d m o d Q 1993 l994 1995 1996 1997 1993 1999 2000 20m 2002 2003 l39iii39iuuliy u im39 m i in mhyim m WMrimmi mum quot Mquot WMquot quot v quot 5quot 3 Linmil ileum iII IiI m i n I Aerosol production rates for most important aerosol types Aerosol Indirect Effects Clouds are formed when water condenses on preexisting aerosol 7 Activation amp Kohler theory in Lecture 20 7 Clouds both re ect and absorb large amounts of radiation slide 8 7 If aerosol changes cloud can change Eg Twomey effect or 15 indirect effect 7 More particles 7 Same H20 7 Smaller droplets 7 Closer to solar wavelenghts so more scattering gt cooling SemiDirect Slimwave Radiative E krl Longwnre Radiative Effcc Cleur Sky Hydrological Ej l39lr Many 1nd1rect effects Indirect Shortwave Radiative E feds Aerosols in uence cluud prapvrriex More droplets gt Brighter Clouds Twomey More droplets gt Enhanced cloud litetime Albrecht More droplets 4 Narrowing of drop distribution W warming Lin Absorbing aerosol hen air and evaporates clouds Hansen Greenhouse effect of aerosol particles Vogclmann Suppressed surface evaporation Spinning down the water cycle Displaced precipitation Clouds last longer or evaporate tRuscnt cld Additional reading Global indirect aerosol effects a review U Lohrnann and J Feichter Atmos ChemPhys571577372005httpwwwatmoschemphysmgacp5715 a Want Where are we with forcings and uncertainties I Tntat so a m mm mm m M ran via my my vmy vary a m Ltm Lu W w W w w g g Level cl Saaarnr Undergarmva r r E E a a 5 g 39 3 E a 2 7 ml 9 E E r Aerosol E E E m at lvu 39 chiw ig n t l 3 9 W5quot lint a 0st an g g m m m t i m e 3939 Lu t K g D srnrwara org a i E g E m a a g 2 3 t snumm It ram a in mm 5 a 0 t r 1 at E E a a l a a s 5 Change


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