Chemistry Reference
In-Depth Information
Table 3 Estimates for mineral dust concentrations for regional and urban background in north-
west Germany, based on different calculation equations (reprinted from [
7
] with permission from
Elsevier)
Model
g/m
3
) Mean urban (
g/m
3
)
Included compounds
Mean regional (
m
m
PMF MinDust
All measured
1.7
4.3
Crustal sum
Mg, Ca, Si, Ti, K, nss-Na
1.2
3.1
Crustal sum + Fe Mg, Ca, Si, Ti, K, bss-Na, Fe 1.4
4.7
IMPROVE
Al, Ca, Si, Ti, Fe (K)
1.5
5.3
RIVM
Al, Si
1.0
2.5
nss-Ca
2+
Tracer
Ca, Na
0.7
2.1
Ca
2+
Tracer
Ca
0.8
2.2
Al Tracer
Al
1.5
3.8
3.3.2 Sea Salt
The impact of sea salt, based on sodium measurements, on the PM concentrations
has been evaluated in numerous studies throughout Europe and compared to model
results [
55
]. Sea salt sodium concentrations clearly depend on the distance to
coastal areas, with a concentration range from
<
0.1
m
g/m
3
at continental sites
g/m
3
close to the shores. In Germany, higher sea salt fractions in PM
are only observed during westerly wind directions and high wind speeds. High
turbulence interconnected with the high wind speed also lead to fast dilution of
emissions. Hence, the sea salt fraction is inversely correlated with PM mass
concentration and only has minor effects on the exceedance of PM limit values [
7
].
and
3
m
>
3.3.3 Mineral Dust
Mineral dust (MD) is a ubiquitous PM component generated by multiple sources
including natural wind erosion, agriculture and other anthropogenic activities (e.g.
construction works, re-suspension by traffic). Its natural elemental composition
consists of Si, Al, Ca, K, Ti, Fe, Na (non-sea-salt) and oxygen, as most of the
compounds are found in form of their oxidic minerals.
A number of different calculation schemes have been developed for the assess-
ment of the mineral dust PM fraction (Table
3
). Some of these schemes are valid
only for sites with negligible anthropogenic influence, since, e.g. the use of Fe as
tracer may lead to an overestimation in environments influenced by traffic or steel
industry. Si and Al are known as the most suitable tracer components [
8
] as they
represent most of the MD mass and have hardly any anthropogenic source except
fly ash from coal combustion [
56
]; however, both components are not commonly
measured in German air quality networks. For regional and remote background
situations also water soluble Ca was shown to be a suitable tracer [
7
,
57
]. In an
eastern German study the MD contribution was calculated from Ti values, a method
which for other, more industrialised regions with titanium production or processing
may lead to overestimation.
