Chemistry Reference
In-Depth Information
is given of the natural versus anthropogenic contributions to PM in north-western
Europe. It is based on the prevalence of major constituents in the chemical mass
closure while incorporating specifics of the region considered.
Sea spray emissions are the most important natural source of primary sulphate.
Applying the sodium-to-sulphate ratio in seawater learns that roughly 5% of the
particulate sulphate is of marine origin. Though sulphate may be emitted directly into
the atmosphere [
17
], its major source is the oxidation of sulphur dioxide. In north-
western Europe, anthropogenic SO
2
emissions are derived mostly from the combus-
tion of sulphur-containing fuels for power generation and international shipping. In
Europe, natural emissions for SO
2
include volcanoes, but given location, height and
distance to the Netherlands, their contribution is probably low (i.e. not more than 1%
to ground level sulphate). Contributions of other biogenic sources of SO
2
like
oxidation of DMS, COS and H
2
S are also of minor importance [
16
]. Wildfire
emissions of SO
2
are commonly neglected in studies directed to wild land fire
emissions. In the approximation here 5% is used as a conservative estimate. To
estimate how much of the nitrate is natural, emissions from soil, biomass burning and
lightning should be considered. Studies on NO emissions from soil report emissions
between 59 and 190 kton in the EU15 ([
17
,
30
]). Relative to the total inventoried
emissions, the central value is 4%. From these emissions, about two-third is attributed
to agricultural soils and one-third to forest soils. Soil NO
x
emissions largely depend
on the nutrient input (through fertilisation or atmospheric deposition) implying that
the abovementioned contribution is only partly natural. Lightning depends linearly on
the amount of convective precipitation. In Europe, corresponding emissions are
estimated to be about 1% (65 kton) of the total inventoried emissions. It mainly
takes place between 1 and 5 km altitude and mostly in southern Europe (Friedrich
et al. 2008). Wild fires estimates range between 20 and 50 kton (Friedrich et al. 2008;
[
18
]) and occur mostly in countries around the Mediterranean. Given the short life
time of NOx and the rather short transport distance of nitrate, we assume that
lightning and wild land fires can be neglected as sources in north-western Europe.
In the approximation here, the natural fraction of NO
x
emissions and therewith nitrate
is taken between 0% and 5%.
Ammonium in aerosols originates from the neutralisation of sulphuric and nitric
acid by ammonia. Ammonia is emitted by different sources, most notably animal
manure, traffic and application of fertiliser. In general, emissions are for the largest
part (80-95%) associated with agricultural activities [
19
]. Erisman et al. [
20
]
estimated the natural emissions at about 10% of the total emissions in Europe. This
percentage includes contributions from wild animals and wetlands. We assume a
similar percentage for ammonium in north-western Europe.
The main source of elemental carbon is the (incomplete) combustion of fossil
fuels. Wild land fires are occasional sources of vast amounts of carbonaceous
particles. Though wild land fires may seem natural, the vast majority of present-
day fires are due to human behaviour. Hence, elemental carbon is almost exclu-
sively anthropogenic.
Organic matter contains numerous chemical constituents of which only a small
fraction has been identified. Organic carbon is released by the incomplete combus-
tion of fuels but in addition originates from farming activities (stables, harvesting)
