1. Multicompartment modelling of POPs
TFMM, Zagreb, April 2005
Multicompartment modelling of POPs
Victor Shatalov, MSC-East
EMEP/MSC-E

2. Outline Model description.
TFMM, Zagreb, April 2005
Outline
Model description.
Sensitivity analysis with respect to pollutant-specific and environmental parameters.
EMEP/MSC-E

3. List of chemicals PAHs (B[a]P, B[b]F, B[k]F)
Model description
TFMM, Zagreb, April 2005
List of chemicals
PAHs (B[a]P, B[b]F, B[k]F)
PCBs (PCB-28, 52, 101, 138, 153, 180)
PCDD/Fs (17 toxic congeners)
Lindane ( -HCH)
HCB
New substances (BDE 47, 99, dicofol, …)
EMEP/MSC-E

4. Model structure Model description
TFMM, Zagreb, April 2005
Model structure
Atmosphere: Gas/particles partitioning, advective transport, diffusion, degradation
regional: 50×50 km
hemispheric: 2.5º ×2.5º
Atmospheric buffer
Exchange between media: wet deposition (gas + particles), dry particulate deposition, gaseous depositions to the underlying surface (soil, seawater, vegetation), re-emission from the underlying surface
Dioxin only one
Soil buffer
Sea buffer
Vegetation buffer
Soil: Partitioning, transport with convective water fluxes, diffusion, bioturbation, degradation.
Seawater: Partitioning, advective transport, diffusion, sedimentation, degradation.
Vegetation: Defoliation, transport to soil, degradation.
EMEP/MSC-E

5. Model description
TFMM, Zagreb, April 2005
Atmosphere
advective transport and turbulent diffusion (presentation on HMs)
gas/particle partitioning
degradation
EMEP/MSC-E

6. Description of processes
Model description
TFMM, Zagreb, April 2005
Description of processes
Gas/aerosol partitioning (Junge-Pankow model)
φ = c · θ / (pOL + c · θ),
φ – fraction of aerosol phase
c – constant = 0.17 Pa · m
θ – specific surface of aerosol particles, m2/m3
pOL – subcooled liquid vapor pressure, Pa
Degradation in the atmosphere (reaction with OH)
dCa/dt = – kd2 · [OH] · Ca,
Ca – air concentration in gaseous phase, ng/m3
[OH] – concentration of OH-radical, molec/m3
kd – degradation rate constant, m3/molec/s.
EMEP/MSC-E

7. Soil partitioning between gaseous, solid and dissolved phases
Model description
TFMM, Zagreb, April 2005
Soil
partitioning between gaseous, solid and dissolved phases
vertical transport due to convective water fluxes, diffusion and bioturbation
degradation
EMEP/MSC-E

8. Partitioning in soil and gaseous exchange
Model description
TFMM, Zagreb, April 2005
Partitioning in soil and gaseous exchange
Instantaneous equilibrium
dCa/dt = k(Cd – Ca)
dCd/dt = k(Ca – Cd)
k – exchange rate coefficient
Ca – concentration of accessible form
Cd – concentration in deeply sorbed form
Partitioning in soil
EMEP/MSC-E

9. Vertical profile of soil concentrations
Model description
TFMM, Zagreb, April 2005
Vertical profile of soil concentrations
Calculated PCB-153 vertical soil concentration profiles in comparison with measurements at three locations in the UK; relative units 2 4 6 8 10
0.2
0.4
0.6
0.8 1
depth, cm
calculated
park grass
moorland
woodland
Measurements taken from: Cousins I.T., B.Gevao and K.C.Jones, Chemosphere, v.39, No.14, 1999
EMEP/MSC-E

10. Seawater Model description
TFMM, Zagreb, April 2005
Seawater
advective transport with sea currents and turbulent diffusion
partitioning between dissolved and particulate phases
sedimentation
degradation
Velocities of sea currents (cm/s), upper sea layer, January 1
Isolines of mixed layer depth (m), January
EMEP/MSC-E

11. Vegetation Model description
TFMM, Zagreb, April 2005
Vegetation
defoliation and transfer to the upper soil layer
degradation
Three types of vegetation: deciduous forest
coniferous forest
grass
Information on Leaf Area Index (LAI) with monthly resolution
EMEP/MSC-E

12. Exchange processes Model description
TFMM, Zagreb, April 2005
Exchange processes
wet deposition (gas + particles) – similar to HM model
dry particulate deposition – similar to HM model
gaseous depositions to underlying surface (soil, seawater, vegetation)
re-emission from environmental media
Ecosystem-dependent scheme
Resistant analogy
EMEP/MSC-E

13. Program flow Model description Start Calculating fluxes between media
TFMM, Zagreb, April 2005
Program flow
Start
Calculating fluxes between media
Determination of time steps
Filling in flux buffers
Assimilating atm. fluxes
Atmospheric module
Assimilating veg. fluxes
Vegetation module
Assimilating soil fluxes
Soil module
Assimilating sea fluxes
Sea module
End
EMEP/MSC-E

14. Model input and output Model description
TFMM, Zagreb, April 2005
Model input and output
Sensitivity analysis
Emphasis: atmospheric concentrations and depositions. Media are used to take into account re-emission process.
EMEP/MSC-E

15. Sensitivity: definitions
Sensitivity study
TFMM, Zagreb, April 2005
Sensitivity: definitions
List of input parameters used in the model is determined
For each input parameter A:
ABase (model value) A
Range of A
ALow
AHigh
DA = (AHigh – ALow)/ABase – relative deviation of A
Air concentrations
Depositions
Sa = DCa/DA; DCa = (CaHigh – CaLow)/CaBase
Sd = DD/DA; DD = (DHigh – DLow)/DBase
Sensitivities of model output with respect to A:
EMEP/MSC-E

16. Pollutant-specific parameters
Sensitivity study
TFMM, Zagreb, April 2005
Pollutant-specific parameters
Exemplified by PCB-153
Parameter
Notation
Base value
Range
Henry’s law constant at 10 ºC, Pa·m3/mol KH
3.8
1.2 – 12.0
Subcooled liquid vapor pressure at 10 ºC, Pa
pOL
9.7·10-5
3.1·10-5 – 3.1·10-6
Octanol/air partitioning coefficient at 10 ºC
KOA
3.6·1010
1.2·1010 – 1.2·1011
Octanol/water partitioning coefficient
KOW
7.9·106
2.5·106 – 2.5·107
Washout ratio for particulate phase Wp
1.5 ·105
4.7·105 – 4.7·106
Mass transfer coefficient to vegetation (deciduous forest), 1/s
KAVdec 30
9.5 – 95
Mass transfer coefficient to vegetation (coniferous forest), 1/s
KAVcon
4.6
1.5 – 15
Degradation coefficient, 1/s Kd
1.2 ·10-7
3.7 ·10-8 – 3.7 ·10-7
Order of magnitude (e.g. 1.2 – 12.0 for KH)
EMEP/MSC-E

17. Environmental parameters
Sensitivity study
TFMM, Zagreb, April 2005
Environmental parameters
Parameter
Notation
Base value
Range
Atmospheric aerosol specific surface, m2/m3 θ
1.5·10-4
1.5·10-5 – 1.5·10-3
Ambient air temperature, °C T 10
0 – 20
Concentration of OH radicals in the atmosphere, molecules/cm3
COH
1.0·106
1.0·105 – 5.0·106
Precipitation amount, mm/hour
Prec
0.1
0.01 – 0.5
Organic carbon fraction in soil
foc
0.05
0.01 – 0.1
Range is chosen in accordance with model input data
EMEP/MSC-E

18. Sensitivity of model output
Sensitivity study
TFMM, Zagreb, April 2005
Sensitivity of model output
Air concentrations of PCB-153, pg/m3
“Low” value of Henry’s law coefficient
“High” value of Henry’s law coefficient
Point source
EMEP/MSC-E

19. Sensitivity of model output
Sensitivity study
TFMM, Zagreb, April 2005
Sensitivity of model output
Sensitivity of air concentrations with respect to Henry’s law coefficient: Sa = DCa/DKH
Sensitivity of depositions with respect to Henry’s law coefficient: Sd = DD/DKH
Point source
EMEP/MSC-E

20. Sensitivity of model output: deposition processes
Sensitivity study
TFMM, Zagreb, April 2005
Sensitivity of model output: deposition processes
Input parameters (pollutant-specific and environmenal)
Vd = Vdwet + Vdpart + Vdsoil · φsoil + Vdsea · φsea + Vdveg · φveg
Output parameters (air concentrations and depositions)
φsoil, φsea, φveg – fractions of soil, sea and vegetation surfaces in a cell
Underlying surface: average for Europe
EMEP/MSC-E

21. Sensitivity of processes
Sensitivity study
TFMM, Zagreb, April 2005
Sensitivity of processes
Gaseous deposition to soil
Gaseous deposition to vegetation
Gaseous deposition to seawater
Wet deposition (gas + particles)
Re-emission
EMEP/MSC-E

22. Gaseous deposition to soil: temperature dependence
Sensitivity study
TFMM, Zagreb, April 2005
Gaseous deposition to soil: temperature dependence
Deposition velocity of direct gas flux Vdgsoil = fgsoil / (Cagas + Capart)
0.0
0.1
0.2
0.3
0.4
0.5 5 10 15 20 25 30
Temperature, C
Deposition velocity, cm/s
0.6
0.8
1.0
Gas fraction
Deposition velocity
1 / Resist
The temperature dependence is investigated
EMEP/MSC-E

23. Gaseous deposition to soil
Sensitivity study
TFMM, Zagreb, April 2005
Gaseous deposition to soil
Parameters used for model description:
Henry’s law constant KH
Octanol/water partitioning coefficient KOW
Vapor pressure over subcooled liquid pOL
Atmospheric aerosol specific surface q
Organic carbon fraction in soil foc
EMEP/MSC-E

24. Sensitivity to Henry’s law constant KH
Sensitivity study
TFMM, Zagreb, April 2005
Sensitivity to Henry’s law constant KH
0.1
0.2
0.3
0.4 5 10 15 20 25 30 T , o C
Base
Low KH
High KH
Deposition velosity, V d
gsoil
, cm/s
0.2
0.4
0.6
0.8 5 10 15 20 25 30 T , o C
Sensitivity, S
gsoil
Variations of deposition velocity
Sensitivity: Sgsoil = D Vdgsoil / DKH,
D – relative deviation
EMEP/MSC-E

25. Gaseous deposition to soil: sensitivity
Sensitivity study
TFMM, Zagreb, April 2005
Gaseous deposition to soil: sensitivity
0.2
0.4
0.6
Henry's law
coeff
Octanol/water
part. coeff
Vapor
pressure
Temperature
Fraction of OC
Specific
aerosol surf.
Sensitivity
Pollutant-related
parameters
Environmental
Sensitivities Sgsoil of Vdgsoil with respect to selected parameters:
Sgsoil = D Vdgsoil / DA
EMEP/MSC-E

26. Wet deposition Sensitivity study Parameters Result (sensitivity of Vd)
TFMM, Zagreb, April 2005
Wet deposition
Parameters
Washout ratio for particulate phase
Subcooled liquid vapor pressure
Henry’s law coefficient
Precipitation rate
Atmospheric aerosol specific surface
Result (sensitivity of Vd)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Washout
ratio
Vapor
pressure
Henry's law
coeff
Temperature
Precipitation
rate
Specific
aerosol
surf.
Sensitivity
Pollutant-related
parameters
Environmental
EMEP/MSC-E

27. Re-emission flux from soil
Sensitivity study
TFMM, Zagreb, April 2005
Re-emission flux from soil
Result (sensitivity of flux)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Octanol/water
part. coeff
Henry's law
coeff
Vapor
pressure
Sensitivity
Parameters
Octanol/water partitioning coefficient
Henry’s law coefficient
Subcooled liquid vapor pressure
EMEP/MSC-E

28. Sensitivity of model output
Sensitivity study
TFMM, Zagreb, April 2005
Sensitivity of model output
0.02
0.04
0.06
0.08
0.1
Kavdec
WashP KH
KOA0
pOL0
KOW
Kavconif
Degr0
Temperature
Precip
foc
OH conc
Theta
Pollutant-related
parameters
Environmental
0.16
Dependence of sensitivity on the distance from the source
Sensitivities of air concentrations averaged over 1000 km from the source
EMEP/MSC-E

29. Uncertainty of model output
Sensitivity study
TFMM, Zagreb, April 2005
Uncertainty of model output
Under above assumptions on uncertainties of input parameters:
Air concentrations
Depositions
Pollutant-specific parameters only
30%
40%
With environmental parameters
50%
70%
In reality uncertainties could be less
EMEP/MSC-E

30. Influence of re-emission from soil
Sensitivity study
TFMM, Zagreb, April 2005
Influence of re-emission from soil
DCa = (Cam – Ca0)/Cam · 100%,
where
Cam – concentration calculated taking re-emission into account
Ca0 – concentration calculated without re-emission
Contribution DCa of re-emission to air concentrations
EMEP/MSC-E

31. TFMM, Zagreb, April 2005
Conclusions
Model output (air concentrations and depositions) is mostly sensitive to to washout ratio for particulate vvphase and Henry’s law constant Among environmental vvparameters the ambient temperature plays essential vvrole.
High spatial variability is characteristic of sensitivity of model output with respect to all considered parameters.
The influence of re-emission process is significant after long-term period of POP application especially in the remote regions.
EMEP/MSC-E

32. Thank you for your attention!

33. Distribution of pollutants between media
Model description
TFMM, Zagreb, April 2005
Distribution of pollutants between media
Dioxin only one
PCB-153: is mainly accumulated in soil
has essential fractions of both particulate and gaseous phases
Emphasis to:
the atmosphere soil
EMEP/MSC-E

34. Model structure Model description
TFMM, Zagreb, April 2005
Model structure
Atmosphere
Underlying surface
Model versions: regional (EMEP), 50 × 50 km
hemispheric, 2.5° × 2.5°
EMEP/MSC-E

35. Temperature dependence
Model description
TFMM, Zagreb, April 2005
Temperature dependence
Fraction of particulate phase
Degradation half-life in air 0%
20%
40%
60%
80%
100% 1 6 11 16 21 26 31 36 41 46 51 T, o C
Fraction of particulate phase
PCB-28
PCB-153
PCB-180 50
100
150
200
250
300
-20
-15
-10 -5 5 10 15 20 25 30 T, o C T
1/2
, days
PCB-28
PCB-153
PCB-180
EMEP/MSC-E