Chapter 8 The atmospheric environment. Figure 8-1. The U.S. Standard Atmosphere, 1976. Note the...
-
date post
19-Dec-2015 -
Category
Documents
-
view
213 -
download
0
Transcript of Chapter 8 The atmospheric environment. Figure 8-1. The U.S. Standard Atmosphere, 1976. Note the...
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).
TroposphereWell-mixed
ozone
Increasing temphere because of proximity to O3 layer
The atmosphere
Little mixingbetween the troposphere andstratosphere
Atmospheric gas composition
Nitrogen, oxygen, argon, neon, xenon constant on 1000 yr timescaleOxygen varies on geologic timescalesCarbon dioxide, nitrous oxide, methane increasingNear surface ozone increasingStratospheric 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 unitsurface 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-wavelengthOutgoing 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 = T4
The wavelength of the maximum emitted energy varies inversely with the temperature and is described by the Wien displacement law:
M = 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
Coriolis Effect
Fc = (2sin)v
Where is the angular velocity of the earth’s rotation in radians (7.29 x 10-5 rad s-1), 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.
Boston, MA latitude 42°23’ N
Death Valley, CA 36°34’N
Khartoum, Sudan 15°62’N
George town, Bahamas 23°51’ N
Macapá, Brazil 0°02’N
Wellington, New Zealand 41°26’S
Capitán Arturo Prat, Antarctica 62°33’
Reykjavik, Iceland 64°8’
Hydrostatic Equation: p = -gh
where p is the change in pressure, is the density of the fluid, g is the acceleration due to gravity, and h 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 evaporationVOCs, 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
Table 8-2. Classification of air pollutants
Major Class Subclass Examples
Inorganic gases Oxides of nitrogen N2O, NO, NO2
Oxides of sulfur SO2 , SO3
Oxides of carbon CO, CO2
Other inorganics O3 , H2S, HF, NH3, Cl2 , Rn
Organic gases Hydrocarbons Methane ( CH4), butane (C4H10), octane (C8H18),benzene (C6H6), acetylene (C2H2), ethylene (C2H4)
Aldehydes and ketones For maldehyde, acetone
Other organ ics Chlorofluorocarbons, PAHs, alcohols, organic acids
Particulates Solids Fume, dust, smoke, ash, carbon soot, lead, asbestos
Liquids Mist, spray, oil, grease, acids
AerosolsSolid particles or liquid droplets ranging in size up to 20um in radius. Caneither be put into the air directly or created in atm
SO2(g) + H2O H2SO4(l) Sulfuric acid aerosol
Table 8-3. Sources of aerosols an d contributions of natural versus anthropogenicsources*
SourceNatural
(1012 g y-1)Anthropogenic
(1012 g y-1)
Soil and rock dust 3000 - 4000 ?
Sea salt 1700 - 4700
Biogenic 100 - 500
Biomass burning (soot) 6 - 11 36 - 154
Volcanic 15 - 90
Direct emissions - fuel, incinerators, industry 15 - 90
Gaseous emissions
Su lfate from biogenic DMS 51
Su lfate from volcanic SO2 18 - 27
Su lfate from fossil fuel 105
Nitrate from NOx 62 128
Ammonium from NH3 28 37
Biogenic hydrocarbons 20 - 150
Anthropogenic hydrocarbons 100
Total 5000 - 9619 421 - 614
*Modified from Berner and Berner (1996)
Factoid: Following large volcanic eruptions, the sulfuric acid aerosol in the atmincreases the earth’s albedo leading to temporary global cooling
Table 8-3. Sources of aerosols an d contributions of natural versus anthropogenicsources*
SourceNatural
(1012 g y-1)Anthropogenic
(1012 g y-1)
Soil and rock dust 3000 - 4000 ?
Sea salt 1700 - 4700
Biogenic 100 - 500
Biomass burning (soot) 6 - 11 36 - 154
Volcanic 15 - 90
Direct emissions - fuel, incinerators, industry 15 - 90
Gaseous emissions
Su lfate from biogenic DMS 51
Su lfate from volcanic SO2 18 - 27
Su lfate from fossil fuel 105
Nitrate from NOx 62 128
Ammonium from NH3 28 37
Biogenic hydrocarbons 20 - 150
Anthropogenic hydrocarbons 100
Total 5000 - 9619 421 - 614
*Modified from Berner and Berner (1996)
Smog
Smoke + fogMore prevalent during inversions
Photochemical smogs – maximum during midday
Table 8-4. Types of s mogs an d their characteristics
Characteristic Industrial Photochemical
First occurrence London Los Angeles
Principal pollutants SOx O3, NOx, HC, CO, free radicals
Principal sources Industrial and household fuel combustion Motor vehicle fuel combustion
Effect on humans Lung and throat irritation Eye and respiratory irritation
Effect on compounds Reducing Oxidizing
Time of worst events Winter months in the early morning Summer months around midday
Industrial smog – mostly acid aerosols, corrode buildings and retinas
Photochemical smogs – mostly formation of ozone, NOx, and PAN, respiratory distress
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 concentrationRate of increase in the atmosphereAtmospheric residence time
Table 8-5. Data for greenhouse gases*
GasConcen tration1990 (ppmv)
Positiveradiativeforcing(W m-2)
% total radiativeforcing
Lifetime(y)
Relativeinstantaneous
radiative forcing(molecular basis)
GlobalW armingPotential(100 y)
CO2 354 1.5 61 50 - 200 1 1
CH4 1.72 0.42 17 12 43 21
H2O strat - 0.14 6
N2O 0.310 0.1 4 120 250 310
CF C-11 0.00028 0.062 2.5 65 15,000 3,400
CF C-12 0.000484 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
CF4 50,000 6,500
C6F14 3,200 7,400
*From Berner and Berner (1996), IPCC (1996), vanLoon and Duffy (2000)
CO2
Figure 8-8. Mean monthly concentrations of CO2 at Mauna Loa, Hawaii. From Berner and Berner (1996).
Imbalance = (fossil fuel) – (increase in CO2) – (ocean storage) + (deforestation)
The ‘missing’ carbon sink. The global CO2 budget is out of balance. We wouldpredict more increase in atm CO2 than what is actually observed.
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).
Fast
slow
Net reaction for atm CO2 uptake in ocean
CO2 + CO32- H2O + 2HCO3
-
Global C box modelRead Case Study 8-2
Methane2nd most important greenhouse gasSinks for methane:
1) chemical oxidation in the troposphere2) stratospheric oxidation3) 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).
Table 8-7. Sources an d sinks for at mos pheric methane*
Source or Sink CH4 (1012 g C y-1) % total
Sources
Natu ral
Wetlands 86 22.5
Termites 15 3.9
Oceans 8 2.1
Lakes 4 1.0
Methane hydrates 4 1.0
Total natural 117 30.5
Anthropogenic
Energy production/use 69 18.0
Enteric fer mentation 63 16.4
Rice 45 11.8
Animal wastes 20 5.2
Landfills 29 7.6
Biomass burning 21 5.5
Domestic sewage 19 5.0
Total anthropogenic 266 69.5
Total fo r sources 383
Sinks
Atmospheric removal 353 88.2
Removal by soils 23 5.8
Atmosphere 24 6.0
Total fo r sinks 400
*Data from Berner and Berner (1996), IP CC (1992)
Methane
How could 14C help tell usThe source of atm methane?
Nitrous Oxide…its no laughing matter
N2O
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 coresStable isotopesDirect gas measurement of bubbles
Figure 8-11. Variation in temperature, CO2, and CH4 concentrations in Antarctica during the past 240,000 years. From Lorius et al. (1993).
Paleotemp fromisotopes
Climate Change and the Geologic Record
Sediment recordStable isotopes (oxygen and/ carbon)
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.
Oxygen isotopes in carbonatesfrom a sediment core in the WesternPacific
Several glacial / interglacial periods
OzoneGood ozone – stratosphereBad ozone – troposphere
Ozone production requires energy from photons
O2 + hv O* + O*
O* + O2 + M O3 (M is a catalyst …e.g. N; HR0 = -106.5 exothermic)
Net reaction …3O2 + hv 2O3
Ozone destruction also involves photonsO3 + hv O2 + O*O* + O3 O2 + O2
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).
Why good ozone is good.
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.
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.
Maximal ozone will form where form where gas molecule density and uv photondenisty are optimal.
Figure 8-14. Altitude versus variations in photon and molecular densities. The optimum altitude for ozone formation occurs where these curves cross.
Ozone layer
Stratospheric ozone distributionHigher over poles (stratospheric transport)Higher in summer vs. winter
The ozone hole
Figure 8-15. Seasonal variation of ozone concentrations (in Dobson units) at Halley Bay, Antarctica, for two different time periods. From Solomon (1990).
Hole varies in size dueto meteorological factors
Additions of N2O,CFCs, and bromineCompounds caused thedecline in ozone
Ozone destroying reactions
N2O
N2O + O* 2NONO + O3 NO2 + O2
NO2 + O NO + O2
O + O3 2O2
CFCl3
Cl’ + O3 ClO’ + O2
ClO’ + O Cl’ + O2
O + O3 2O2
CFCl3 + hv CFCl2’ + Cl’
For each of these reactionsthe Cl’ and the NO return to theiroriginal state. They are catalystsonly and do not participate in the reaction
Calculating reaction rates for various ozone destroying chemicals
Example 8-3: Calc reaction rate for Cl’ + O3 ClO’ + O3 at 235K.Cl’ conc. = 5.0 E11. O3 conc = 2.0 E12. Reaction rate = k [Cl][O3]
-Calc k using Arrhenius eqnk = Ae-Ea/RT
k = (2.8 E-12 cm3 molecules-1 s-1)e –(21 KJ mol-1)(8.314 kJ mol-1K-1)(235K)
k= 6.0 e-17 cm3 molecules-1 s-1
-Rate calcrate = (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 ozonePhotochemical smogOH radicals or NO is a catalyst for the production of troposhperic ozone
NO (nitric oxide) released during fuel combustionNO converted to NO2 by a host of reactions
NO2 + hv NO + OO + O2 + M O3 + M …remember M is a catalytic particle
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).
Of which, O3 is one
Radon – 222Rn
Produced from the 238U decay chainProblematic when bedrock contains uranium
218Po and 214Po progeny are particle active, particles inhaled, lodged in lungs…subsequent alpha decay damages lung tissue
Consider Rn levels inside:Generalized steady state equation for an inside pollutant
Ri = kexCi – kexCo
Ci = Co + Ri/kex
Ci = inside concCo = outside conckex = exchange coefRi= production rate of pollutant
Since Rn is radioactive, the expression is modified to acct. for decay
Ri= kex Ai + Ai – kexA0
Ai= (Ri + kexA0 ) / (kex + )
Indoor activity of Rn is:
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 + )
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 ChemistryCompounds found in rainwater come from seawater, terrestrial or pollution sources
Table 8-10. Sources of individual ions in rainwater*
Origin
Ion Marine inputs Terrestrial inputs Pollution inputs
Na+ Sea salt Soil dust Biomass burning
Mg2+ Sea salt Soil dust Biomass burning
K+ Sea salt Biogenic aerosolsSoil dust
Biomass burningFertilizer
Ca2+ Sea salt Soil dust Cement manufactureFuel burningBiomass burning
H+ Gas reaction Gas reaction Fuel burning
Cl- Sea salt None Industrial HCl
SO2
4 Sea saltDMS from biologicaldecay
DMS, H2S, etc., frombiological decayVolcanoesSoil dust
Biomass burning
NO
3 N2 plus lightning NO2 from biological decayN2 plus lightning
Auto emissionsFossil fuelsBiomass burningFertilizer
NH
4 NH3 from biologicalactivity
NH3 from bacterial decay NH3 fertilizersHuman, animal wastedecomposition(Combustion)
PO3
4 Biogenic aerosols adsorbedon sea salt
Soil dust Biomass burningFertilizer
HCO
3 CO2 in air CO2 in airSoil dust
None
SiO2, Al, Fe None Soil dust Land clearing
*From Berner and Berner (1996)
SO2
4
NO
3
NH
4
PO3
4
HCO
3
Cl- in rain is assumed tobe from a seawater source
Cl- and other ions in fromseawater are assumed to have a constant proportion
Rain sample can be ‘corrected’for seawater contribution
Excess ion X = total ion X – [(ratio of ion X to Cl- in seawater) (Cl- conc)]
Table 8-11. Weight ratios of major ions in seawater relative to Cl-- or Na++*
Ion W eight ratio to Cl- Weight ratio to Na+
Cl- 1.00 1.80
Na+ 0.56 1.00
Mg2+ 0.07 0.12
SO2
4 0.14 0.25
Ca2+ 0.02 0.04
K+ 0.02 0.04
*Source of data for ratio calculations, Wilson (1975)
Mg2+
SO2
4
Ca2+
Table 8-12. Primary associations for rainwater*
Origin Association
Marine Cl - Na - Mg - SO4
Soil Al - Fe - Si - Ca - (K, Mg, Na)
Biological N O3 - NH4 - SO4 - K
Biomass burning N O3 - NH4 - P - K - SO4 - (Ca, Na, Mg)
Industrial pollution SO4 - NO3 - Cl
Fertilizers K - PO4 - NH4 - NO3
*From 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
Marine influence on rainwater chemistry
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).
SeawaterCl- /Na+ = 1.8
Low ratios reflectdust inputs from sodium-richrocks
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 depositionand 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).
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).
Two most important species for acid rainare nitrate and sulfate
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 andNitric 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
Chemistry and sources of atmospheric particulates (aerosols)
Figure 8-24. Sources of atmospheric particulates. Arrows with dashed lines indicate that there is a gaseous emission associated with the source.
Primarily tropospherictransport
Mineral dustFine particlesAeolian transportSahara dust
Trace element delivery to remote oceans (e.g. Antarctica)
Sea Salts
Bursting of bubblesPure sea salt aerosols have a predictable ratio of the major ions in seawater
Cl/Na , S/Na , N/Na
SulfatesSulfate 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 particleBlack carbon (soot) – incomplete combustion
Soot from coal (fly ash) = high K, Fe, Mn, ZnSoot from oil = high V
Organic aerosols- VOCsBioaerosols – spores, pollen, and volatile bio-organic compounds (Blue mountains)
Dry deposition – dust settlingRate determined by radius of particle (Stokes Law)
Wet deposition – washoutPrecip (rain or snow)Condensation
Aerosols serve as condensation nuclei for the formation ofclouds
Source tracking for aerosol deposition
Air mass trajectoriesUsing atmospheric circulation models to reconstruct the history of anair 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 crustalConcentration
Assume that the particulate conc. of Al, Fe, Si, Ti, or Sc are solely from the crustal contribution.
Calc EFcrust the crustal Enrichment Factor
XRE particulate
XRE crust
EFcrust=X = conc. of element XRE = conc. of reference element
Calculating the noncrustal conc. of element X
Xnoncrustal=XRE crust
- REparticulateXtotal
Table 8-14. Elemental composition of the continental crust*
Concentration (ppm) Concentration (ppm)
Element Upper crust Bulk crust Element 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 3000 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 1.0
*Data from Taylor and McLennan (1985). Both bulk continental crust and upper continentalcrust have been used to calculate crust ratios. In some cases the results may differsignificantly. For example, the Pb/Al ratio for the upper crust is 2.5 x 10 -4 while for the bulkcrust the ratio is 9.5 x 10 -5. Given a sample that has a Pb/Al ratio of 2.5 x 10 -4, the upper crustgives an EF of 1 while the bulk crust gives an EF of 2.6. The difference is great enough thatdifferent conclusions might be drawn regarding the source of the Pb (natural for upper crustnor malization and anthropogenic fo r bulk crust normalization). Cr would show an evengreater 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 = 5suggesting 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
XRE particulate
XRE crust
EFcrust=
71,000 particulate
18584,100 crust
= = 3.2
Xnoncrustal=XRE crust
- REparticulateXtotal
Crnoncrustal= 18584,100- 10007
Crnoncrustal = 4.8 ppm
Elemental, molecular and isotopic signatures are used to source aerosols from crust, marine, or pollution sources
X = Xcrust + Xmarine + Xpollution
Using Al, Na, and Se, for reference elements for crust, marine, and pollution sourcesrespectively...
XAl crust
AlXSe pollution
SeXNa marine
NaX = + +
To solve for a particular component, divide both sides of equation by the ref elementfor that component. Ex: Crust
XAl crust
AlXSe pollution
SeXNa marine
NaX = + +
Al Al AlAl
Elemental
Pairwise plotting of the elemental ratios (X/Al, X/Na, X/Se) shows the contributionsof the different sources graphically
100% crustalsource
100% marinesource
100% crustalsource
100% pollutsource
Molecular signatures
‘Fingerprints’ mostly for VOCs
CPI (carbon preference index) = #odd carbon chains / #even carbon chainspetroleum= 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 usedto derive other ratios.
Example 8-10: Aerosol sample: 206Pb/204Pb = 18.004, 208Pb/204Pb = 38.08, what’s the 208Pb / 206Pb ratio?
(208Pb/204Pb)(206Pb/204Pb) = 38.08/18.004 = 2.115
3 endmember mixing applied to lead isotopes
(207Pb/206Pb) meas = (207Pb/206Pb)a fa + (207Pb/206Pb)b fb + (207Pb/206Pb)c fc
Need two markers and 3 equations
1)
(206Pb/208Pb) meas = (206Pb/208Pb)a fa + (206Pb/208Pb)b fb + (206Pb/208Pb)c fc 2)
3) fa + fb + fc = 1
See Example 8-11
Isotopic signatures
Example: 14C
Percent modern carbon (pmc) = 0.95 x 14C content of a standard
Nuke bomb testing added a lot of 14C to the atm. This excess is decaying andthe atm is not in equilibrium with respect to 14C
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%