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Chapter 8 The atmospheric environment The atmosphere Little mixing between the troposphere and stratosphere ozone Increasing temp here because of proximity to O3 layer Troposphere Well-mixed Figure 8-1. The U.S. Standard Atmosphere, 1976. Note the various temperature reversals, which act as thermal lids on the lower parts of the atmosphere. In the troposphere, gases are well mixed. From Neiburger et al. (1982). Atmospheric gas composition Nitrogen, oxygen, argon, neon, xenon constant on 1000 yr timescale Oxygen varies on geologic timescales Carbon dioxide, nitrous oxide, methane increasing Near surface ozone increasing Stratospheric ozone (ozone layer) decreasing Very upper atmosphere has gradients in each gas due to gravity effect on the different molecular weights Solar Radiation and Atmospheric Heating Solar constant – measure of the amount of energy passing through a unit surface area perpendicular to the direction of the solar radiation Albedo – amount of energy reflected back to space from the surface and the Atmosphere Insolation – amount of energy reaching the earth’s surface Incoming solar radiation is short-wavelength Outgoing solar radiation is long-wavelength Any gas with multiple bonds will absorb some long-wavelength radiation and turn it into heat…..greenhouse gas Water vapor, carbon dioxide, nitrous oxide, methane, CFCs Venus… It is estimated that the surface temperature on Venus would actually be below 0°F without the Greenhouse effect. However, because of the greenhouse effect, the average surface temperature is 467°C or 872°F. Atmospheric Composition at Surface Level Major Components (by volume) CO2 96.5% N2 3.5% Minor Component (ppm) SO2 150 Ar 70 H2O 20 CO 17 He 12 Ne 7 Perfect Radiator: any substance that emits the maximum amount of electromagnetic energy at all wavelengths. Total amount of energy emitted is a function of temperature and described by the Stefan-Boltzmann law: E = sT4 The wavelength of the maximum emitted energy varies inversely with the temperature and is described by the Wien displacement law: lM = aT-1 Short wavelength radiation: general term for radiation coming from the sun. Long wavelength radiation: general term for radiation coming from the earth. There is a latitudinal disequilibrium of heat on the planet Figure 8-4. Incoming (shortwave) and outgoing (longwave) radiation as a function of latitude. The crossover occurs at ~40o. At lower latitudes there is a heat excess, at higher latitudes a heat deficit. Yet the heat flux of the planet is just about in steady state. Heat redistributed due to atmospheric (and oceanic) circulation Global Redistribution of Heat through circulation without the spin of the Earth Coriolis Effect Fc = (2Wsinf)v Where W is the angular velocity of the earth’s rotation in radians (7.29 x 10-5 rad s-1), f is the latitude, and v is the velocity of the moving mass. Note that at the equator the Coriolis force would be zero, and at the poles the Coriolis force would be at its maximum value. Global Atmospheric Circulation with the spin of the Earth Polar Cell Ferrel Cell Ferrel Cell Reykjavik, Iceland 64°8’ Boston, MA latitude 42°23’ N Death Valley, CA 36°34’N George town, Bahamas 23°51’ N Khartoum, Sudan 15°62’N Macapá, Brazil 0°02’N Wellington, New Zealand 41°26’S Capitán Arturo Prat, Antarctica 62°33’ Hydrostatic Equation: Dp = -rgDh where Dp is the change in pressure, r is the density of the fluid, g is the acceleration due to gravity, and Dh is the change in height. Dry adiabatic lapse rate: the rate at which an air parcel cools if lifted in the atmosphere or warms if forced to lower levels, as long as no condensation occurs in the air parcel. (= ~9.8 K km-1.) Absolute humidity: the amount of water vapor actually present in the air. Relative humidity: the amount of water vapor in the air divided by the amount of water vapor the air can hold at any particular temperature, expressed in percent. Wet adiabatic lapse rate: the rate at which an air parcel cools when condensation occurs. It is a function of temperature and pressure. Environmental lapse rate: the observed rate at which temperature changes in a column of air. Inversion: the reversal of the normal temperature pattern Radiation inversion: caused by radiational cooling of the land surface and a decrease in the temperature of the atmosphere at low levels. Subtropical inversion: caused by sinking air at high pressure center. *Remember, when air descends its temperature increases. Frontal inversion: caused by the relative movement of warm air over cold air. Air Pollution Primary pollutants – direct products of combustion or evaporation VOCs, CO, CO2, SOx, NOx Secondary pollutants – products of atmospheric reactions involving primary pollutants Ozone, compounds produced by photochemical oxidation (PANs: Peroxyacytyl nitrate) VOCs and NOx’s are important reactants in forming secondary pollutants Ta ble 8-2. Classification of air pollutants Major Class Sub class Inorganic gases O xides of nitrogen N 2 O, NO, N O 2 O xides of sulfur SO 2 , SO 3 O xides of carbon CO, CO 2 Other ino rganics O 3 , H 2S, HF, N H 3, Cl 2 , Rn Hydro carbons M ethane ( CH 4), butane (C4 H 10 ), octane (C8 H 18), benzene (C6 H 6), acetylene (C2 H 2), ethylene (C2 H 4) Aldehydes and ketones For maldehyde, acetone Other organ ics Chlorofluo rocarbons, PA Hs, alcohols, organic acids Solids Fu me, dust, smoke, ash, carbon soot, lead, asbestos Liquids M ist, spray, oil, grease, acids Organic gases Particulates Examp les Aerosols Solid particles or liquid droplets ranging in size up to 20um in radius. Can either be put into the air directly or created in atm SO2(g) + H2O H2SO4(l) Sulfuric acid aerosol Ta ble 8-3. Sour ces of aerosols an d c ontri butions of natural versus anthr opog enic sourc es* Natural (1 0 12 g y -1) An throp ogenic (1 0 12 g y -1) Soil and rock dust 3000 - 4000 ? Se a salt 1700 - 4700 Sou rc e Biogenic 100 - 500 Bio mass burning (soot) 6 - 11 Volca nic 15 - 90 Dire ct e missions - fuel, inc inerators, industry 36 - 154 15 - 90 Gaseous e missions Su lfa te fro m bioge nic DMS Su lfa te fro m volc anic SO 2 51 18 - 27 Su lfa te fro m fossil fuel 105 Nitrate fro m NO x 62 128 A mmoniu m fro m NH 3 28 37 Biogenic hydroca rbons 20 - 150 Anthropogenic hydroca rbo ns Tota l 100 5000 - 9619 421 - 614 * Modified from Be rne r and Be rner (1996) Factoid: Following large volcanic eruptions, the sulfuric acid aerosol in the atm increases the earth’s albedo leading to temporary global cooling Ta ble 8-3. Sources of aerosols an d contri butions of natural versus anthropog enic sources* Natural (1 0 12 g y -1) An throp ogenic (1 0 12 g y -1) Soil and rock dust 3000 - 4000 ? Sea salt 1700 - 4700 Biogenic 100 - 500 Sou rce Bio mass burning (soot) 6 - 11 Volcanic 15 - 90 Direct emissions - fuel, incinerators, industry 36 - 154 15 - 90 Gaseous emissions Su lfate fro m biogenic DMS Su lfate fro m volcanic SO 2 51 18 - 27 Su lfate fro m fossil fuel 105 Nitrate fro m NO x 62 128 A mmoniu m fro m NH 3 28 37 Biogenic hydrocarbons 20 - 150 Anthropogenic hydrocarbo ns Total * Modified from Berner and Berner (1996) 100 5000 - 9619 421 - 614 Smog Smoke + fog More prevalent during inversions Photochemical smogs – maximum during midday Ta ble 8-4. Types of s mogs an d their characteristics Characteristic Industrial Photoch emical First occurrence Londo n Los Angeles Principal pollutants SO x O 3 , NO x, H C, CO, free radicals Principal sou rces Industrial and h ousehold fuel co mbustion M otor vehicle fuel comb ustion Effect on hu mans Lung and throat irritatio n Eye and respiratory irritation Effect on co mpounds Reducing O xidi zing Time of worst events Winter mo nths in the early morning Su mmer months aroun d midday Industrial smog – mostly acid aerosols, corrode buildings and retinas Photochemical smogs – mostly formation of ozone, NOx, and PAN, respiratory distress The Great London Smog of 1952 Greenhouse Gases: CO2, CH4, N2O & CFCs that absorb long-wave, out-going radiation causing them to vibrate and generate heat. Positive and negative feedbacks of greenhouse effect and climate change Hotter world = more water vapor = more heat trapping = positive feedback Hotter world = more cloud cover = less insolation = negative feedback Hotter world = less snow = less albedo = more net insolation = postive feedback Hotter world = faster decomp = more CO2 = more heat trap = positive feedback More CO2 + temp = more photosynthesis = less CO2 = negative feedback Geologic record indicates periods of warm wet earth and cold dry earth The relative effect of an individual gas on the greenhouse effect over time depends upon: Molecular scale radiative forcing (how well it converts radiation to heat) Atmospheric concentration Rate of increase in the atmosphere Atmospheric residence time Ta ble 8-5. Data for greenhouse gases* Gas Concen tration 1990 (ppmv) CO 2 35 4 Positive radiative forcing (W m-2) % total radiative forcing Relative instantan eous Lifeti me radiative forcing (y) (molecular basis) Global W arming Potential (100 y) 1.5 61 50 - 200 1 1 12 43 21 310 CH 4 1.72 0.42 17 H 2 O strat - 0.14 6 N2 O 0.310 0.1 4 120 250 CF C-11 0.00028 0.062 2.5 65 15,000 3,400 CF C-12 0.00048 4 0.14 6 130 19,000 7,100 Other CFCs 0.085 3.5 Total 2.45 100.0 CF C substitutes HFC-23 264 650 HFC-152a 1.5 140 50,000 6,500 3,200 7,400 CF 4 C6 F1 4 *Fro m Berner and Berner (1996), IPCC (1996), van Loon and Duffy (2000) CO2 Imbalance = (fossil fuel) – (increase in CO2) – (ocean storage) + (deforestation) The ‘missing’ carbon sink. The global CO2 budget is out of balance. We would predict more increase in atm CO2 than what is actually observed. Figure 8-8. Mean monthly concentrations of CO2 at Mauna Loa, Hawaii. From Berner and Berner (1996). Read Case Study 8-2 Global C box model Net reaction for atm CO2 uptake in ocean CO2 + CO32- H2O + 2HCO3- Fast slow Figure 8-9. The carbon cycle. Reservoir concentrations are in 1015 g (Gt) carbon. Fluxes are in Gt C y-1. From Berner and Berner (1996). Methane 2nd most important greenhouse gas Sinks for methane: 1) chemical oxidation in the troposphere 2) stratospheric oxidation 3) microbe uptake Figure 8-10. Variation in methane abundance from 1841 to 1996. The fitted curve is a sixth-order polynomial. Data from Etheridge et al. (1994) and IPCC (1966). Methane Ta ble 8-7. Sourc es an d sinks for at mos phe ric methane* Source or Sink CH 4 (10 1 2 g C y -1) % tota l Sources Natu ra l How could 14C help tell us The source of atm methane? Wetla nds 86 22.5 Te rmites 15 3.9 Ocea ns 8 2.1 La kes 4 1.0 Me thane hydrates 4 1.0 117 30.5 Ene rgy production/use 69 18.0 Ente ric fer menta tion 63 16.4 Rice 45 11.8 Ani mal wastes 20 5.2 La ndfills 29 7.6 Bio mass burning 21 5.5 Do mestic sewa ge 19 5.0 266 69.5 Total natural Anthropoge nic Total anthropoge nic Total fo r sou rc es 383 Sin ks At mosphe ric re moval 353 88.2 Re moval by soils 23 5.8 At mosphe re 24 6.0 Total fo r sinks 400 * Data fro m Berne r and Be rne r (1996), IP CC (1 992) Nitrous Oxide…its no laughing matter N 2O Sources: denitrification, nitrification, biomass burning & fertilizer production No N2O sinks in the troposphere The third largest contributor to global warming behind CO2 and CH4. Also responsible for stratospheric ozone destruction. Climate Change and the Geologic Record Ice cores Stable isotopes Direct gas measurement of bubbles Paleotemp from isotopes Figure 8-11. Variation in temperature, CO2, and CH4 concentrations in Antarctica during the past 240,000 years. From Lorius et al. (1993). Climate Change and the Geologic Record Sediment record Stable isotopes (oxygen and/ carbon) Oxygen isotopes in carbonates from a sediment core in the Western Pacific Several glacial / interglacial periods Figure 8-12. Surface temperature of the Pacific Ocean based on oxygen isotope ratios. From THE BLUE PLANET, 2nd Edition by B. J. Skinner, S. C. Porter and D. B. Botkin. Copyright © 1999. This material is used by permission of John Wiley & Sons, Inc. Ozone Good ozone – stratosphere Bad ozone – troposphere Ozone production requires energy from photons O2 + hv O* + O* O* + O2 + M O3 (M is a catalyst …e.g. N; DHR0 = -106.5 exothermic) Net reaction …3O2 + hv 2O3 Ozone destruction also involves photons O3 + hv O2 + O* O* + O3 O2 + O2 Why good ozone is good. Figure 8-13. Absorption cross sections for oxygen and ozone in the 100 to 300 nm wavelengths. Also shown is the solar flux density and the wavelengths of biologically harmful radiation (UV-B and UV-C). From vanLoon and Duffy (2000). The polar vortex is a persistent, large-scale cyclone located near the Earth's poles, in the middle and upper troposphere and the stratosphere. It surrounds the polar highs and is part of the polar front. Nitric acid in polar stratospheric clouds reacts with CFCs to form chlorine, which catalyzes the photochemical destruction of ozone. Chlorine concentrations build up during the winter polar night, and the consequent ozone destruction is greatest when the sunlight returns in spring (September/October). These clouds can only form at temperatures below about -80°C, so the warmer Arctic region does not have an ozone hole. Maximal ozone will form where form where gas molecule density and uv photon denisty are optimal. Ozone layer Figure 8-14. Altitude versus variations in photon and molecular densities. The optimum altitude for ozone formation occurs where these curves cross. Stratospheric ozone distribution Higher over poles (stratospheric transport) Higher in summer vs. winter The ozone hole Hole varies in size due to meteorological factors Additions of N2O, CFCs, and bromine Compounds caused the decline in ozone Figure 8-15. Seasonal variation of ozone concentrations (in Dobson units) at Halley Bay, Antarctica, for two different time periods. From Solomon (1990). Ozone destroying reactions N2O N2O + O* 2NO NO + O3 NO2 + O2 NO2 + O NO + O2 O + O3 2O2 CFCl3 CFCl3 + hv CFCl2’ + Cl’ Cl’ + O3 ClO’ + O2 ClO’ + O Cl’ + O2 O + O3 2O2 For each of these reactions the Cl’ and the NO return to their original state. They are catalysts only and do not participate in the reaction Calculating reaction rates for various ozone destroying chemicals Ta ble 8-8. Kin etic data for variou s re actan ts in th e catalytic des tru ction of ozon e at 235 K* X + O3 X Concen tration ( molecu les cm-3) A (cm3 molecules -1 s -1) Ea (kJ mol-1) k 235 (cm3 molecules -1 s-1 ) O 1.0 x 10 9 H 2.0 x 10 1 5 1.4 x 10 -10 3.9 1.9 x 10 -11 OH 1.0 x 10 6 1.6 x 10 -12 7.8 3.0 x 10 -14 NO 5.0 x 10 8 1.8 x 10 -12 11.4 5.3 x 10 -15 Cl Very small 2.8 x 10 -12 21 6.0 x 10 -17 XO + O XO Calc reaction Concen tration rate forA Cl’ + O ClO’ E Example 8-3: + O3 at k235K. 3 ( molecu les cm ) (cm molecules s ) (kJ mol ) (cm molecules s ) Cl’ conc. = 5.0 E11. O3 conc = 2.0 E12. Reaction rate = k [Cl][O3] a -3 3 -1 -1 235 -1 3 -1 O2 5.0 x 10 1 6 8.0 x 10 -12 17.1 1.3 x 10 -15 HO 1.0 x 10 6 2.3 x 10 -11 0 2.3 x 10 -11 7 -11 -11 19 -12 -12 7 -11 -11 -1 -Calc k using Arrhenius eqn HO 2.5 x 10 2.2 x 10 -0.1 2.3 x 10 k =NOAe-Ea/RT 5.0 x 10 9.3 x 10 0 9.3 x 10 -12 3 -1 -1 –(21 KJ mol-1)(8.314 kJ mol-1K-1)(235K) k =ClO (2.8 E 2.0 cmx 10 molecules s )e 4.7 x 10 0.4 3.8 x 10 3 -1 s-1 k=*The6.0 e-17 cm con centrations of themolecules species are for an altitude of 30 k m with the exception of ClO which is for an 2 2 -Rate calc altitude of 35 km. The co ncentration of o zone at 30 k m is 2.0 x 1 0 12 mo lecules cm-3. Fro m van Loon and Du ffy (20 00) rate = (6.0 E-17 cm3 molecules-1 s-1)(5.0 E11 molecules cm-3)(2.0 E12 molecules cm-3) rate = 6.0 E7 molecules cm-3 s-1 Tropospheric ozone Bad ozone Photochemical smog OH radicals or NO is a catalyst for the production of troposhperic ozone NO (nitric oxide) released during fuel combustion NO converted to NO2 by a host of reactions NO2 + hv NO + O O + O2 + M O3 + M …remember M is a catalytic particle Of which, O3 is one Figure 8-16. Variation in abundances of various species, on a 24-hour cycle, produced during a photochemical smog event. From vanLoon and Duffy (2000). Radon – 222Rn Produced from the 238U decay chain Problematic when bedrock contains uranium and 214Po progeny are particle active, particles inhaled, lodged in lungs… subsequent alpha decay damages lung tissue 218Po Consider Rn levels inside: Generalized steady state equation for an inside pollutant Ri = kexCi – kexCo Ci = Co + Ri/kex Ci = inside conc Co = outside conc kex = exchange coef Ri= production rate of pollutant Since Rn is radioactive, the expression is modified to acct. for decay Ri= kex Ai + lAi – kexA0 Indoor activity of Rn is: Ai= (Ri + kexA0 ) / (kex + l) Example 8-4: Radon release from soils to a basement at a rate of 0.01 Bq L-1 h-1 Outdoor air has Rn acitivity of 4.0 E-3 Bq L-1 h-1. Assume air exchange coeff of 10 h-1 What is the steady state indoor actvitiy of Rn? Ai= (Ri + kexA0 ) / (kex + l) Plug and chug…answer is Ai = 5.0 E-3 Bq L-1 h-1 Radon flux depends on any factors that change gas diffusion -soil moisture -temp (solubility of Rn) -freezing (caps Rn) -barometric pressure Rn is elevated in groundwaters and can be used as a tracer for gw inputs to Surface waters Rainwater Chemistry Compounds found in rainwater come from seawater, terrestrial or pollution sources T a ble 8 - 1 0 . S o u rces o f in di vi du a l io n s in ra in wa t er * Origin Ion Ma rine inputs Te rrestrial inputs Pollution inputs Na+ Sea salt Soil d ust Biomass burning Mg 2+ Sea salt Soil d ust Biomass burning K+ Sea salt Bioge nic aerosols Soil d ust Biomass burning Fertilize r Ca2 + Sea salt Soil d ust Ce ment ma nufacture Fuel burning Biomass burning H+ Gas rea ction Gas re action Fuel burning Cl - Sea salt None Industrial H Cl Sea salt DM S from biologica l dec ay DM S, H 2S, etc ., fro m biologica l de cay Volc anoes Soil d ust Biomass burning N 2 plus lightning NO 2 fro m biologic al de cay N 2 plus lightning Auto e missions Fossil fu els Biomass burning Fertilize r NH 3 from biologica l activity NH 3 fro m bac terial deca y NH 3 fertilize rs Hu man , ani mal waste de co mposition (Co mbustion) Bioge nic a erosols adsorbe d on sea salt Soil d ust Biomass burning Fertilize r HC O3 CO 2 in air C O 2 in air Soil d ust None Si O 2, Al, Fe None Soil d ust Land clea ring 2 SO 4 NO 3 NH 4 3 PO 4 Cl- in rain is assumed to be from a seawater source Cl- and other ions in from seawater are assumed to have a constant proportion Rain sample can be ‘corrected’ for seawater contribution *Fro m Berner a nd Berner (199 6) Excess ion X = total ion X – [(ratio of ion X to Cl- in seawater) (Cl- conc)] Ta ble 8-11. W eigh t r atios of major ions in s ea wate r r elati ve to C l-- or N a++ * Ion W eight ratio to Cl - Weight ratio to Na+ Cl- 1.00 1.80 Na + 0.56 1.00 M g 2+ 0.07 0.12 SO 4 0.14 0.25 Ca2+ 0.02 0.04 K+ 0.02 0.04 2 *So urce of data for ratio calculations, Wilson (1975) Ta ble 8-12. P ri mary as s oci ation s for r ain w ater* Origin Association Marin e Cl - Na - M g - SO 4 Soil Al - Fe - Si - Ca - (K, M g, Na) Biological N O 3 - NH 4 - SO 4 - K Bio mass burning N O 3 - NH 4 - P - K - SO 4 - (Ca, Na, Mg) Industrial pollution SO 4 - NO 3 - Cl Fertilizers K - PO 4 - NH 4 - NO 3 *Fro m Berner and Berner (1996) Figure 8-17. Average Cl- concentration (mg L-1) of rainwater for the United States from July 1955 to June 1956. From Berner and Berner (1996). Marine influence on rainwater chemistry Low ratios reflect dust inputs from sodium-rich rocks Seawater Cl- /Na+ = 1.8 Figure 8-18. Average Cl-/Na+ weight ratio of rainwater for the United States from July 1955 to June 1956. From Berner and Berner (1996). Marine influence on rainwater chemistry Gaseous species SO2(g) + 2OH(g) H2SO4(aq) 2 H+ + SO42- gas phase SO2(g) + H2O2(aq) H2SO4(aq) 2H+ + SO42- liquid droplets NO2(g) + OH(g) HNO3(aq) H+ + NO3- NH3(g) + H2O NH4OH(aq) NH4+ + OH- Acid deposition and what else? Figure 8-19. Global SO2 produced by the burning of fossil fuel, 1940 to 1986, in Tg SO2 S y-1 (1 Tg = 106 metric tons = 1012 g). From Berner and Berner (1996). Figure 8-20. Global NOx produced by the burning of fossil fuel, 1970 to 1986, in Tg NOx - N y-1. From Berner and Berner (1996). Figure 8-21. Generalized isoconcentration contours for SO42- (in mg L-1) for atmospheric precipitation over the contiguous United States in 1995. Source of data is the NADP. From Langmuir (1997). Figure 8-22. Generalized isoconcentration contours for NO3- (in mg L-1) for atmospheric precipitation over the contiguous United States in 1995. Source of data is the NADP. From Langmuir (1997). Two most important species for acid rain are nitrate and sulfate Figure 8-23. Average pH for precipitation in 1955-1956 and 1972-1973 for the northeastern United States and Canada and in 1980 for the contiguous United States and Canada. From Langmuir (1997). Example 8-7: Calc pH for a stream receiving acid rain. Calc moles of sulfate and nitrate (from Table 8-13) sulfate = 2.165 E-5 mol L-1 nitrate = 2.355 E-5 mol L-1 Calculate H+ produced based on what you know about the normality of sulfuric and Nitric acid. One mole H+ per mole nitrate, two moles H+ per mole sulfate. Moles H+ = 6.685 E-5 mol L-1 pH = -log [H+] = 4.17 The Nitrogen Cycle Hog Production in USA (1 dot= 10,000 Hogs and Pigs) Chemistry and sources of atmospheric particulates (aerosols) Primarily tropospheric transport Figure 8-24. Sources of atmospheric particulates. Arrows with dashed lines indicate that there is a gaseous emission associated with the source. Mineral dust Fine particles Aeolian transport Sahara dust Trace element delivery to remote oceans (e.g. Antarctica) Sea Salts Bursting of bubbles Pure sea salt aerosols have a predictable ratio of the major ions in seawater Cl/Na , S/Na , N/Na Sulfates Sulfate aerosols can be in the form of (NH4)2SO4, or H2SO4 primarily Sources: Anthropogenic - combustion Natural – DMS (dimethyl sulfide), volcanoes (SO2 and H2S) Carbon-derived particle Black carbon (soot) – incomplete combustion Soot from coal (fly ash) = high K, Fe, Mn, Zn Soot from oil = high V Organic aerosols- VOCs Bioaerosols – spores, pollen, and volatile bio-organic compounds (Blue mountains) Dry deposition – dust settling Rate determined by radius of particle (Stokes Law) Wet deposition – washout Precip (rain or snow) Condensation Aerosols serve as condensation nuclei for the formation of clouds Source tracking for aerosol deposition Air mass trajectories Using atmospheric circulation models to reconstruct the history of an air mass. Aerosol : Crust Enrichment Factor Determination of the amount of additional element that has been added to a particulate above that amount which you would expect based upon its crustal Concentration Assume that the particulate conc. of Al, Fe, Si, Ti, or Sc are solely from the crustal contribution. Calc EFcrust the crustal Enrichment Factor X RE particulate EFcrust= X = conc. of element X RE = conc. of reference element X RE crust Calculating the noncrustal conc. of element X Xnoncrustal= Xtotal - REparticulate X RE crust Ta ble 8-14. Ele men tal co m pos ition of th e c on tin e ntal cru s t* Concen tration (pp m) Element Concentration (pp m) Upper crust Bulk crust Al 80,400 84,100 Se 0.05 0.05 Fe 35,000 70,700 Mo 1.5 1.0 Sc 11 30 Ag 0.050 0.080 Ti 3 000 5400 Cd 0.098 0.098 V 60 230 Sn 5.5 2.5 Cr 35 185 Sb 0.2 0.2 Mn 600 1400 W 2.0 1.0 Co 10 29 Au 0.0018 0.003 Ni 20 105 Pb 20 8.0 Cu 25 75 Th 10.7 3.5 Zn 71 80 U 2.8 0.91 As 1.5 Element Upp er crust Bulk Crust 1.0 *Data fro m Taylor and McLen nan (19 85). Both bulk co ntinental crust an d upper contin ental crust have been used to calculate crust ratios. In some cases the results may differ significantly. For example, the Pb/Al ratio for th e up per crust is 2.5 x 1 0 -4 while for the bulk crust the ratio is 9.5 x 10 -5. Given a samp le that has a Pb /Al ratio of 2.5 x 10 -4, th e up per crust gives an EF of 1 while the bulk crust gives an EF of 2.6. The difference is great eno ugh that different conclusions might b e drawn regarding the source of the Pb (natu ral for upp er crust nor malization and anth ropogenic fo r bulk crust normalization). Cr would sho w an even greater difference, but in the opposite sense. The Cr/Al ratio for the upper crust is 4.4 x 10-4 while for the bulk crust the ratio is 2.2 x 10 -3. Given a sample with a Cr/Al ratio of 2.2 x 10 -3, the bulk crust normalization gives EF = 1 while the upper crust nor malization gives EF = 5 suggesting that there is an anthropogenic contribution to the Cr content of the sample. Example 8-9: Aerosol sample has 1000ppm Al and 7ppm Cr. Calculate the crustal enrichment factor and the noncrustal concentration of Cr X RE particulate 7 1,000 EFcrust= particulate = 3.2 = X RE crust 185 84,100 Xnoncrustal= Xtotal - REparticulate Crnoncrustal = 7 - 1000 Crnoncrustal = 4.8 ppm X RE 185 84,100 crust crust Elemental, molecular and isotopic signatures are used to source aerosols from crust, marine, or pollution sources Elemental X = Xcrust + Xmarine + Xpollution Using Al, Na, and Se, for reference elements for crust, marine, and pollution sources respectively... X = Al X Al + Na crust X Na + Se marine X Se pollution To solve for a particular component, divide both sides of equation by the ref element for that component. Ex: Crust X = Al Al Al X Al crust + Na Al X Na + Se marine Al X Se pollution Pairwise plotting of the elemental ratios (X/Al, X/Na, X/Se) shows the contributions of the different sources graphically 100% crustal source 100% marine source 100% crustal source 100% pollut source Molecular signatures ‘Fingerprints’ mostly for VOCs CPI (carbon preference index) = #odd carbon chains / #even carbon chains petroleum= CPI = 1, natural compounds = CPI < 1 Chain length ratios, aromaticity, trace compounds, biomarkers Isotopic signatures Lead revisited- multiple lead isotopes that can be ratio-ed to each other and used to derive other ratios. Example 8-10: Aerosol sample: what’s the 208Pb / 206Pb ratio? 206Pb/204Pb = 18.004, 208Pb/204Pb = 38.08, (208Pb/204Pb)(206Pb/204Pb) = 38.08/18.004 = 2.115 3 endmember mixing applied to lead isotopes Need two markers and 3 equations 1) (207Pb/206Pb) meas = (207Pb/206Pb)a fa + (207Pb/206Pb)b fb + (207Pb/206Pb)c fc 2) (206Pb/208Pb) meas = (206Pb/208Pb)a fa + (206Pb/208Pb)b fb + (206Pb/208Pb)c fc 3) f a + f b + fc = 1 See Example 8-11 Isotopic signatures Example: 14C Nuke bomb testing added a lot of 14C to the atm. This excess is decaying and the atm is not in equilibrium with respect to 14C Percent modern carbon (pmc) = 0.95 x 14C content of a standard Percent biogenic carbon = ( 14C of sample / 14C atm at time of sampling) x 100 {all 14C measurements in pmc} Example 8-12: Aerosol containing formic acid. 14C in sample = 88.7, 14C in atm = 110.5 %biogenic = (14Cmeas/14C atm) x 100 = (88.7/110.5) x 100 = 80% Happy Thanksgiving!!