1. Institute for Coastal Research / System Analysis and Modelling
6th Meeting of the EMEP Task Force on Measurements and Modelling Zagreb, Croatia, April Approaches to Modelling HMs and POPs Distribution in the Environment
Gerhard Petersen
GKSS Research Centre
Institute for Coastal Research / System Analysis and Modelling
Max-Planck-Strasse 1
D Geesthacht
GERMANY

2. UN-ECE Convention on Long Range Transboudary Air Pollution
Protocols on Heavy Metals and Persistent Organic Pollutants
The Aarhus Protocol on Persistent Organic Pollutants (POPs).
Adopted in 1998, the Protocol on Persistent Organic Pollutants (POPs) entered
into force in October It bans the production and use of some substances
outright, while scheduling others for elimination or severe restriction at a later
stage (aldrin, chlordane, dieldrin, dioxins, endrin, hexabromophenyl, furans,
mirex, PAH, HCH (or lindane) toxaphenes, DDT, heptachlor,
hexachlorobenzene, PCBs).
2. The Aarhus Protocol on Heavy Metals (HMs).
Adopted in 1998, the Protocol on Heavy Metals entered into force in December
2003. It focuses on cadmium, lead and mercury – heavy metals particularly
harmful to human health and the environment.

3. priority metals of concern and their typical concentrations in ambient air over Europe
lead ng m-3
cadmium ng m-3
mercury
Hg ng m-3
HgCl ng m-3
MeHg ng m-3
Hg(part.) ng m-3

4. Observed Ranges of POP Concentrations in Ambient Air 1990 - 1999
in Europe and in Remote Areas (North Atlantic and Arctic)
(adopted from Malanichev et al., 2002)

5. Main Properties of POPs affecting their Long-Range Transport Potential
(adpoted from Malanichev et al., 2002)
* at average scavenging and gas exchange fluxes
** at average scavenging and gas exchange fluxes and 4 m s-1 transport velocity

6. The Approaches to Modelling POPs
(1) Multi-Compartmental Mass Balance Models for POPs
The first approach to describing the distribution of POPs in the environment
are relatively simple mathematical descriptions of the natural environment
designed to simulate the behavior of chemicals, which are likely to be found
in more than one environmental medium or phase.
Such models subdivide the environment into a number of compartments –
well mixed “boxes“, which are assumed to have homogeneous environmental
characteristics and chemical concentrations.
These models tend to
involve multiple environmental compartments.
have a low spatial resolution.
involve simplifying assumptions of equilibrium and steady-state.

7. The Approaches to Modelling POPs
(2) Adapting Atmospheric Dispersion Models to POPs
The second approach to describing the distribution of POPs in the environment
is the adaption of classical air pollution dispersion models to POPS.
These models tend to
be atmospheric models where the Earth‘s surface is a more or less complex
boundary.
have a high spatial resolution with often several thousands grid cells.
be sometimes limited to simulating relatively short time periods on the scale of
weeks and months, although with the increase in computing power even
multi-year calculations have become possible.

8. The Approaches to Modelling POPs
(3) Simulating low volatility POPs with atmospheric dispersion models
Specifically, the group of low volatility POPs, which include the more highly
chlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) are as well as the
polycyclic aromatic hydrocarbons (PAHs) with more than four fused rings,
are distinct, in that:
they are present in the atmosphere essentially completely in the particle phase
and their atmospheric deposition is dominated by particle associated deposition.
their potential for volatilization from soils and vegetation is negligible.
at least for the combustion derived PAHs the emission situation more closely
resembles that of classical air pollutants (no secondary sources, emissions
quantifiable by measurements of various combustion sources etc.).
Atmospheric models, that are capable of simulating the dispersion behaviour of such
particles, should be well suited for the simulation of low volatility POPs.
Box models with limited spatial resolution, on the other hand, are poorly equipped
to describe aerosol transport and deposition in the atmosphere.

9. Evolution of a global distribution model from a simple box model
to a zonally averaged, two-dimensional multimedia model
Wania et al., 1999
McKay et al., 1992
atmosphere
terrestrial
environment
aquatic
cold warm hot
Wania and
McKay , 1992
N-Polar N-Boreal N-Temperate N-Subtropic N-Tropic S-Tropic S-Subtropic S-Temperate S-Polar
Wania and
McKay, 1993
N-Polar N-Boreal N-Temperate N-Subtropic N-Tropic S-Tropic S-Subtropic S-Temperate S-Subpolar S-Polar
Wania et al., 1999

10. The POPCYCLING Baltic Model
aiming to quantify the pathways of POPs from the terrestrial
environment to the marine environment via atmosphere and rivers
(adopted from Wania: Differences, Similarities, and Complementarity of Various Approaches to Modelling
Persistent Organic Pollutant Distribution in the Environment, WMO/EMEP/UNEP Workshop, Geneva, 1999 )

11. A B C Compartmentalisation of the
terrestrial (A), marine (B) and atmospheric (C) environment
of the Baltic Sea Drainage Basin in the POPCYCLING Baltic model
(adopted from Wania: Differences, Similarities, and Complementarity of Various Approaches to Modelling
Persistent Organic Pollutant Distribution in the Environment, WMO/EMEP/UNEP Workshop, Geneva, 1999 ) A B C

12. Spatial scales of atmospheric processes of heavy metals and POPs
European scale.
Motions of whole weather systems, on scales of hundreds to thousands
of kilometers:
Heavy metals (except mercury), PAHs (e.g B[a]P), PCCDs/Fs
Hemispheric and Global scale.
Phenomena occurring on scales exceeding 5 x 103 kilometers:
Mercury, high volatility POPs (e.g. some PCB congeners, HCB)

13. Domain of an Eulerian chemistry and transport model
used within the UNECE CLRTAP
(source: EMEP Meteorological Synthesizing Centre West, Oslo, Norway)

14. ADOM–EUROPE for Heavy Metals model domain
3-d Eulerian grid model
with a time step of
1 hour
rotated spherical
coordinate system
of the HIgh Resolution
Limited Area Weather
Prediction Model
(HIRLAM) with 76 by 76
grid cells
~55x55 km2 grid cell size
12 vertical layers between
1 and m with 8
layers below 2000 m

15. Spatial distribution of PCB-153 deposition in theNorthern Hemisphere
and in the EMEP domain
units: g km-2 a-1
(adopted from EMEP MSC-E Information Note 5/2004)
1990

16. Spatial distribution of PCB-153 deposition in the Northern Hemisphere
and in the EMEP domain
units: g km-2 a-1
(adopted from EMEP MSC-E Information Note 5/2004)
2000

17. Outflow of POPS from the EMEP model domain
(adopted from EMEP MSC-E Information Note 5/2004) %
POP emissions
COMPOUND OUTFLOW
[% of emissions
in the EMEP domain]
B[a]P 20
PCDD/Fs 40
PCBs 50
γ-HCH 75
HCB 80

18. Modelling of heavy metals transport on a hemispheric scale
with the GRAHM model
mercury concentration in surface air January 16, 1997
(Dastoor and Laroque: Global circulation of atmospheric mercury…., Atmos. Env. 38, , 2004 )
Units: ng m-3

19. The Community Multi-scale Air Quality Model (CMAQ):
Emissions and Meteorological Modeling Systems and
the CMAQ Chemical Transport Model and Interface Processor
MM5
Meteorological
Modelling System
SMOKE
Emission
Modelling System
MCIP
Meteorology – Chemistry
Interface Processor
ECIP
Emissions – Chemistry
Interface Processor
LUPROC
Land use Processor
Process
Analysis
CMAQ Chemical Transport Model (CTM)
ICON and BCON
Initial and Boundary
Conditions Processor
Aerosol
Chemistry and
Dynamics
Plume-in-grid
Treatment
Cloud
Governing
Equations
Gas Phase
Chemistry
Transport
Algorithms
Aggregation
JPROC
Photolysis Rate
Processor

20. C The Community Multi-scale Air Quality Model (CMAQ) for Europe
CMAQ Europe
81x90 grid cells
54x54 km2 grid cell size
CMAQ North Sea
55x58 grid cells,18x18 km2 grid cell size
PM10 concentration in air, Sept 21, 2001

21. The Complementarity of the two Approaches
Box models
Box models aim to describe the big picture of a POP‘s fate in the environment
with a focus on large-scale spatial patterns and long-term trends.
The use of average conditions is possible and common and it is conceivable
to simulate the entire lifetime of a POP in a region from initial release to
final degradation, even over several centuries.
Box models deliberately ignore the fine detail and have no capacity to resolve
concentration differences on a small spatial or temporal scale.
Conceivable = denkbar, vorstellbar

22. The Complementarity of the two Approaches
Dispersion models
Dispersion models aim to describe primarily the atmospheric transport
taking into account the highly variable nature of meteorological and transport
conditions.
short term fluctuations on the scale of davs and even hours are resolved.
Rather than aiming to describe long-term averaged conditions dispersion models
are often describing events, such as particular long-range transport episodes.

23. Summary and Conclusions
Box models are appropriate tools to simulate the entire lifetime of
a POP from initial release to final degradation in more than one
environmental medium and phase, even over several centuries.
Current atmospheric dispersion models are well suited for the
simulation of heavy metals and low volatility POPs (e.g. some of the
PAHs and PCDDs/Fs) on time scales of weeks to several years.
In the mid-term future, advanced atmospheric dispersion models like
CMAQ incorporating an extensive treatment of aerosol chemistry and
dynamics and emission processing are expected to play an
increasingly important role,
provided that a more detailed knowledge on HMs and POPs
emissions and atmospheric processes including air/surface
exchange becomes available.