Chemistry Reference
In-Depth Information
2
2
2
primary emissions
regional
wind
4
1
5
3
4
3
3
3
oceans
industrial
areas
agriculture
urban
areas
rural
areas
mountains
and glaciers
5
lakes
latitude
temperature
Fig. 7 Conceptual representation of processes influencing the atmospheric transport and fate of
POPs. (
1
) Primary emissions of POPs to the atmosphere, (
2
) atmospheric deposition and photo-
chemical degradation/transformation, (
3
) re-volatilisation from secondary sources in the different
environmental compartments and burial in sediments, (
4
) bioaccumulation and biotic transport,
(
5
) accumulation in glaciers and ice caps, with probable releases due to melting
capacity of soils and lake sediments depends on several factors, such as its organic
content, ambient temperatures, biological activity, physical disturbance and chem-
ical transformation [
6
,
49
-
53
].
3.1 Gas-Particle Exchange
The exchange of chemical compounds from the gas phase to a surface, e.g.
atmospheric particles, soil, water, vegetation or other surfaces, is controlled by
the affinity of the compound to this surface. The ratio of vapour pressure to water
solubility can be used as indicator between levels in the atmosphere and water
surface (Henry's law;
H
constant). In many model calculations, the ratio between
POP levels in octanol and water, the octanol-water partitioning coefficient (
K
ow
), is
used as reference for the distribution of POP in organic material [
14
]. Conse-
quently, the expression
H
/RT (
C
air
/
C
water
) and
K
ow
(
C
octanol
/
C
water
) provide the
octanol-air partitioning coefficient (
K
oa
):
K
oa
ΒΌ
K
ow
RT
=
H
which can be used as the indicator for the distribution of POP between the
atmosphere and surfaces. Since
H
is temperature-dependent,
K
oa
is temperature-
dependent as well [
54
,
55
].
Vegetation has been used in the past as indicator of the degree of atmospheric
contamination on small and global scale [
44
,
54
,
56
,
57
]. Although important
differences between chemical species have been observed, in general the lipophilic
