Gerhard Lammel: “Trends and Advances in Atmospheric and
Environmental Chemistry"
Budgeting atmospheric processes
Halogenated SOCs and multicompartmental substances
Air-surface mass exchange processes
Trace substance mass budgets, surface cycling:
Emissions, deposition, re-volatilisation
Mass budget equation, residence time
dmi/dt = sources – sinks = Ei – Si = Ei – (ki degrad
(1) + ki dep
(1)) mi = mi/τ
[g/s]
dci/dt = Ei – Si = Fi em/h - (ki degrad
(1) + ki dep
(1)) ci = ci/τair [g/m³/s]
• Chemical loss processes of i are 1st order in ci
• Source processes of i are 0th order in ci
Depositional loss processes are here expressed as 1st order in ci for simplicity
For dmi/dt = 0, the system is called to be chemically in a steady state
dmi/dt = (Fi in + Ei) – (Fi out + Si)
with: Fi in, Fi out = fluxes over boundary
Ei, Si = internal sources and sinks
mi = Mg i/Mg air <xi> mtrop
Mg i, Mg air = molar masses (Mair = 29 g/mol)
<xi> = spatial average of mixing ratio
mtrop = mass of tropospheric air = 4.25× 1015 t
Si = (Σj kij
(2) Nj /V + ji
(1)) Ni/V = kV
(1) Ni/V
with: kji
(2), ji
(1)= rate coefficients, photolysis rates
Ni/V, Nj/V = reaction partner number concentrations
kV
(1) = tropospheric average chemical sink rate coefficient
If well mixed or almost well mixed: advective losses Fi out
Fi out ~ mi = kF mi; with: kF = empiric parameter
dmi/dt = Fi in + Ei + (kF + kV
(1)) mi
τi = (kF + kV
(1))-1; with: τi = residence time (not equal to but < ‚lifetime‘!)
assuming (in 1st approx.) that kV
(1) ≠ f(mi), i.e. no chemical feedbacks
leading to Nj/V = f(Ni/V)
Variability and atmospheric residence time:
Averaging over long times (> mixing times)
steady state-assumption holds: dmi/dt = <Fi in> + <Qi> - (kF + kV
(1)) mi ≈ 0
Ni/V = <Ni/V > + (Ni/V)‘(x, y, z, t);
with: <Ni/V> = temporally and spatially mean number concentration
(Ni/V)‘ = local and temporal number concentration
x, y, z = space coordinates
Empiric finding (Junge, 1974) for the
relative standard deviation
σi = σi*((Ni/V)‘) / <Ni/V > = 0.14/ τi
with: σi* = absolute
standard deviation of (Ni/V)‘
→ The residence time, τi, can be infered
from variability, as σi = f(τi)
Example: non-methane hydrocarbons (NMHC)
Global budget (Tg/a)
Natural 1150 terrestrial vegetation
2 marine biosphere
Anthropogenic 120 of which are:
52 % transport
7 % fossil fuels, stationary
5 % chemical, petrochemical industries
9 % oil and gas production
27 % solvents
(Ehhalt, 1986; Guenther et al., 1996)
• location: mostly from ground, from stacks, from aircrafts
• temporal profile, e.g. diel, weekly, seasonal, historical trends
• spatial distributions
Emissions
Emissions, CH4
(Crutzen & Gidel, 1983)
Global Model results
Tg/10°lat
lat
increase
sources
(Model results: Horowitz et al., 2003; Crutzen & Gidel, 1983)
Global distributions CO (ppbv) @ 970 and 510 hPa, monthly mean
Distributions – spatial, seasonal
Higher levels in the N Pacific (Iwata et al., 1993)
N-S gradient in the Bering and Chukchi Seas
(Jantunen & Bidleman, 1995)
Many (most) semivolatile and persistent organic substances are accumulating in high
latitudes (despite source distribution). Example α-hexachlorocyclohexane (α-HCH)
Halogenated SOCs and multicompartmental substances
Introduction: concerns persistence, bioaccumulation and
effects
Decreasing trends in air, water and sediments
not found in biota:
(AMAP, 2004)
cfish monitoring
Decreasing trends in air and water not necessarily followed in
organisms:
Bioaccumulation along food chains
Bioaccumulation, marine foodweb
Relative proportions of halogenated SOCs in the Barents Sea foodweb (Borga et al., 2001)
PCB-180 in Northwater Polynya foodweb (Fisk et al., 2001)
log KOW = 5.3 3.6-3.8 5-7
Processes of SOCs
pL
0
pL
0 s
s
SPM
DOC
PM
OM
pL
0 s
.
(g)
.
(diss)
(p)
(diss) Kow
Kowk
Kowk
topsoil
surface water
= volatilisation and dry deposition of (gaseous) molecules
Two film model (or: two film theory of gas absorption)
- existence of 2 stagnant layers on either side of the interface (fictitious dimensions)
- provide resistance additively (Liss & Slater, 1974; Schwarzenbach et al., 2002)
- equilibrium established at the interface itself
- gas flux through interface F = -kmt w (cw - cwi) = -kmt g (cgi - cg) [mol/m²/s]
aqueous phase
interface
gas phase
SOCs surface exchange
Air-sea exchange
:= Kaw
F = -kmt w (cw - cwi) = -kmt g (cgi - cg) [mol/m²/s]
cgi = Kaw cwi
with bulk (cw,cg) and equilibrium (cwi, cgi) concentrations in water and air
Resistance by boundary layers: reciprocal transfer coefficient (‚piston velocity‘ kmt w,
kmt g [cm/s])
- defined positive for flux from air to water
- consideration of 1 side sufficient for most gases
dcw/dt = kmt net (cw - cg/Kaw) [mol/s]
R = 1/kmt net = 1/kmt w + 1/(kmt w Kaw) [s/cm]
Parameterisations in models are empirically based.
From known examples to formula for unknown molecule i (molecular mass Mgi):
Kmt g H2O = 0.83 cm/s → kmt g i = 0.83 (18/Mgi)0.5 cm/s
Kmt w CO2 = 0.0056 cm/s → kmt w i = 0.0056 (44/Mgi)0.5 cm/s
(Atlas & Giam, 1986)
Wind dependence:
kw CO2(u) = 0.31 u² (Sc/660)0.5 cm/s (Wanninkhoff, 1992)
Volatilisation (left) and dry deposition (right) result from and correspond to opposite
signs of (cg - cwKaw).
General concept for all interfaces:
Mass flow from phase with higher to phase with lower fugacity.
Fugacity of substance i, fij: = escaping tendency from a phase j ([Pa] or [N/m²])
f/p describes deviation from ideal behaviour, similar to a/c.
(example: molar free enthalpy µ = µ0 + RT ln(p/p0) → µ = µ0 + RT ln(f/p0))
Fugacity capacity Zij: fij = cij/Zij
Ki 12 = ci1/ci2 = Zi1fi1/(Zi2fi2) (Paterson & Mackay, 1985)
fij [Pa]
Fugacity capacity of phase: Zij = cij/ fij
Partitioning coefficients, e.g. Kaw = cg/cw = Zgfg/Zwfw
Examples
Air: cg = n/V = p/RT → cg = fg/RT, Zg = (RT)-1, fg = cg RT
Seawater: Zw=cw/p =1/H‘,
with Henry coefficient H‘ = RTKaw [Pa m³/mol]= 10-2/KH[M/at]
fw = cw/Zw = H‘cw
Air-sea exchange: Fraction of fugacity from seawater = fw / (fw + fg)
Cycling of HCH in the North Sea: Dry deposition vs. volatilisation ?
Observation: declining local emissions
(BSH, 2006)
γ-HCH a -HCH
Sea region Southern North
Sea
German Bight Southern North
Sea
German Bight
Year 1996 2001 1996 2001 1996 2001 1996 2001
Burden
(Sensitivity)
3.03
(13%)
1.39
(5%)
0.31
(40%)
0.18
(27%)
1.17
(66%)
0.45
(74%)
0.14
(16%)
0.04
(25%)
Wet deposition 5.47 1.67 0.35 0.11 0.81 0.22 0.05 0.01
Dry deposition 8.85 2.34 0.76 0.21 8.98 2.56 0.77 0.24
Volatilisation 3.42 1.59 0.61 0.33 4.29 0.98 0.67 0.18
Degradation 0.002 0.001 0.0002 0.0001 0.003 0.001 0.0002 0.0001
Sedimentation 1.96 0.98 0.06 0.03 0.97 0.39 0.03 0.01
Resuspension 0.21 0.10 0.007 0.003 0.05 0.02 0.002 0.001
Dry deposition vs. volatilisation of HCH in the North Sea
Under declining local emissions net-depositional.
γ-HCH, net-volatilisational in the
German Bight (Ilyina et al., 2006)
1996
(a)
-2 0 2 4 6 8
51
52
53
54
55
56
57
1997
(b)
-2 0 2 4 6 8
51
52
53
54
55
56
57
1998
(c)
-2 0 2 4 6 8
51
52
53
54
55
56
57
1999
(d)
-2 0 2 4 6 8
51
52
53
54
55
56
57
2000
(e)
-2 0 2 4 6 8
51
52
53
54
55
56
57
2001
(f)
-2 0 2 4 6 8
51
52
53
54
55
56
57
0.5 1 1.5 2
Vertically integrated annual mean
concentrations of γ-HCH (ng/l)
Dry deposition vs. volatilisation of HCH
in the Bering and Chukchi seas
The isomer α-HCH, upon accumulation
since the 1950s, turned netvolatilisational
in the early 1990s.
(Jantunen & Bidleman, 1995)
α- and γ-hexachlorocyclohexane along a N-S-transect 1999/2000
in air in ocean surface water
gamma-HCH
0.0
0.5
1.0
-90-60-300306090
latitude
Fugacityfractionfw/(fw+fa)
H (Kucklick'91)
H (Sahsuvar'03)
alpha-HCH
0.0
0.5
1.0
-90-60-300306090
latitude
Fugacityfractionfw/(fw+fa)
H (Kucklick'91)
H (Sahsuvar'03)
(Lakaschus et al., 2002)
Fractionoffugacityfromseawater=fw/(fw+fg)
10(10.14-3208/T)
10(10.13-3098/T)
H'(T) [Pa m³/mol]
(Sahsuvar et al., 2003)
10(7.54-2382/T)
10(9.31-2810/T)
H'(T) [Pa m³/mol]
(Kucklick et al., 1991)
γ-HCHα-HCH
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
β-1,2,3,4,5,6-
Hexachlorocyclohexane
γ-1,2,3,4,5,6-
Hexachlorocyclohexane
α-1,2,3,4,5,6-
Hexachlorocyclohexane
Terminology:
• Congeners: compounds of similar but not
identical elemental composition
• Isomers: compounds of same elemental
composition but different structure
• Conformational isomers: Isomers which can be
converted into each other without cleavage of
bonds
• Enantiomers: chiral isomers,
Isomers
Enantiomers α-1,2,3,4,5,6-
Hexachlorocyclohexane
Manufacture of all chiral compounds is as
racemic mixture, (as long as no enzymatic
processes are involved).
An assignment of the absolute structure to (+)and
(-)-enantiomers is not (yet) possible.
Using enantiomeric signatures to study SOC cycling
Enzymatic processes are enantioselective.
→ Degradation of chiral substances often takes place enantioselectively, yielding
nonracemic residues (enantiomeric ratio ER ≠ 1.00). The distinct enantiomeric signatures of
these residues can be used as markers to follow environmental transport and fate processes:
Fraction emitted from one source, A, of 2 possible sources, A, B:
fA = (ERA and B – ERB)x(ERA + 1)/[(ERA - ERB) x(ERA and B + 1)]
(Bidleman & Falconer, 1999)
Examples:
ER of (+)-α-HCH/(-)-α-HCH = 0.85±0.03 in Baltic Sea and 0.87±0.05 in North
Sea waters, because microbial degradation prefers (+)-α-HCH, (while photolytic
degradation is not enantioselective). It seems that part of the α-HCH is formed
from (slow, non-enantioselective) isomerization from γ-HCH. (Hühnerfuss et al.,
1992)
Observation in North Sea air: ER = 0.95 → fvol = 0.37 and fadv = 0.63 for A =
volatilization, B = advection, and with ERvol = 0.87, ERadv = 1.00
Using enantiomeric signatures
Similar air-soil exchange (Fraser Valley, Canada, 1995): Determination of the fraction
volatilizing from contaminated soil vs. advected.
Enantioselective degradation of (+) or (-) o,p'-DDT in soil was accompanied by
enrichment or depletion of the corresponding enantiomers in the overlying air (Bidleman
& Leone, 2004).
cair = f(z) (Finizio et al., 1998)
ER = f(z):
9.2.1.5 Enantioselective chromatography
• Most volatile chiral compounds can be separated in their enantiomers using
cyclodextrin-based capillary GC columns (König, 1984; König et al., 1988).
• Cyclodextrin is a cyclic, chiral, torus shaped macromolecule which contains
D(+)-glucose residues bonded through (1-4)glycosidic linkages. The common
cyclodextrins used in chromatography are the α-, β- and γ-cyclodextrins which
contain 6, 7 and 8 glucose units, respectively. Inside the ring is hydrophobic,
outside hydrophilic.
• Substance classes: mono- and sesquiterpenes, pharmaceuticals, biphenyls and
polychlorinated biphenyls (PCBs), besides other.
GC using an enantioselective chromatographic column:
Fused-silica capillary, coated with 50% heptakis(2,3,8-tri-n-pentyl)-β-cyclodextrin
and 50% polysiloxane (high polarity, OV1701), ECD detection (Hühnerfuss &
Kallenborn, 1992; Hühnerfuss et al., 1992)
Start with (easier!): bioaccumulation in the aqueous
system:
Bioconcentration factor BCF:= ci biota/ci w [ ]
Uptake of polychlorinated biphenyls (PCB; 0.1 mg/l) in 3 algae
species: Kinetics, inter-species variability (Wang et al., 1999)
Vegetation and air
Uptake of neutral organic substances in leaves/needles from the gas-
phase:
- primarily via (wax covered) cuticulae, not stomatae (which enable gas exchange of small,
inorganic molecules), distribution within the plant largely unknown
- partitioning determined by lipophilicity (expressed as the octanol-water partitioning
coefficient Kow), diffusion driven (Tolls & McLachlan, 1994, besides others):
F = v (ainside - aoutside)
log vmembrane = 1.2 log Kow – 7.5 (Grayson & Kleier 1990)
v = D Kav / Δx
log vmembrane = log Kow – 6.7
F = flux (g/m2/s), v = permeability (m/s), a = activity (g/m3),
D = diffusion coefficient ≈ 10-14 m²/s for organics, Kav = air/veg. partitioning coefficient,
Δx = membrane thickness ≈ 0.05 mm
Uptake (continued): Kinetic limitations
- For plants with little permeability equilibrium distribution not achieved within
one vegetation period
F = A-1 dm/dt = v Δc
A = V / Δx
V-1 dm/dt = dci(veg)/dt = Δx kmt
(1) (ci(g)/Kleaf/air - ci(veg))
kmt
(1) = kmt‘(1) Kleaf/air/(S/V)
S/V = leave surface/vol., exchange coefficient Kleaf/air (can vary by several orders of
magnitude for various species, as a function of wax, phyto structure), clearance rate
k‘(1) (determined by volatilisation during photodegradation, degradation slow, for
example < 5%/vegetation period for PCB)
- ‚Kinetically‘ limited due to delays caused by the turbulence of the atmospheric
layers near to the ground and the canopy (for log Kow > 8.2), limited by particle
processes if log Kow > 11 (McLachlan et al., 1995; McLachlan, 1996; Böhme et al., 1999)
(Wania & McLachlan, 2001)
Flux from air to vegetation controlled by (specific) surface, boundary layer
resistance (atmospheric turbulence)
Plant uptake from atmospheric dry
gaseous deposition for hypothetical
substances
(log Koa < 5: no net effect compared
to bare soil)
Gas Phase:
• Diffusion
Water Phase
• Dispersion
• convection
Biological
Phase:
• plant uptake
• microbiological
degradation
Solid Phase:
• diffusion in
aggreagates
• chemical
reactions
leaching
Evaporation
ad/desorption
precipitation
dissolution
volatilization
dissolution
Multiphase system soil
fOM
Upward:
• Gas-phase diffusion within soil pore space
• Aqueous phase diffusion in soil water
• Co-evaporation with water vapour
• Turbulent flow in capillaries
Downward:
• Dry deposition, limited by uptake in soil multiphase system (water, OM, solid surfaces)
Fz = vdep(z) (c(z) – c0)
(Jury et al., 1983)
Air-soil exchange
Air-soil partitioning = f(T, rh)
Soil-air partitioning coefficient KSA=cS/cA
(McLachlan, 2001)
adopted from Wania, 1999
Multicompartmental distribution when phase equilibria were established in the
environment: f(KAW, KOW, KOA)
Multicompartmental modelling approaches
Multicompartmental distribution