Chemistry Reference
In-Depth Information
9,0
7,8
8,0
6,6
7,0
6,0
5,0
4,4
4,3
4,3
NO3
SO4
NH4
4,0
3,9
3,5
4,0
3,4
3,1
3,0
2,4
2,4
2,2
2,2
2,1
1,8
2,0
1,4
1,3
1,0
0,0
urban
rural
urban
rural
urban
rural
NL
B
G
Fig. 3 The urban increment of the SIA components
Like in most cities in Europe, a rise in PM10 concentrations is measured when
moving from rural to urban sites. Clearly, a comparison like this depends on the
selection of sites, in particular distance between sites and surroundings affect
results like these. Here, the increase in PM10 is between 7 and 11
g/m
3
. No single
constituent (or emission source) can be held solely “responsible”: all (including the
unknown part) appear higher at the urban sites, but there is no systematic pattern
observed here. In Belgium and Germany, the increment is largely due to more SIA,
OM+EC and MD (between 2 and 4
m
g/m
3
). In the Dutch data set, however, the
unknown part contributes most. The increase of sea salt at the urban site Schiedam
is due to its location close to the North Sea. The rise of MD is substantial at all sites.
The urban increment observed for SIA systematically returns for each of its
component (Fig.
3
).
It is seen that the increment of SIA is predominantly caused by nitrate (the
Netherlands and Belgium) and sulphate (Germany), while the change for ammo-
nium is modest. Levels of nitrate and sulphate are usually higher in urban or
industrial areas in Europe [
14
,
15
]. In marine and coastal atmospheres, nitric acid
is converted into particulate nitrate (NaNO
3
) through the reaction with sea-salt
particles resulting in the release of HCl: NaCl + HNO3
!
NaNO3 + HCl. In
contrast to NH
4
NO
3
, NaNO
3
is a non-volatile compound under atmospheric
conditions; therefore, partitioning of nitric acid into the sea salt is irreversible.
A similar reaction applies for sulphuric acid (and sulphate). Most of the nitrate here
is found in the fine mode as ammonium nitrate (and ammonium sulphate).
m
3 Anthropogenic and Natural Contributions to PM
in North-Western Europe
Important for air pollution policy in Europe is the contribution to PM10 that is of
anthropogenic origin. It is this fraction that can be targeted by national and
European abatement strategies. Below, a first-order rather pragmatic assessment
