Chemistry Reference
In-Depth Information
Fig. 3 Key features of submicron aerosol measured at Central European and North Italian
EUSAAR and GUAN stations. (a) location of the stations, (b) key features of size distributions,
(c) key factors of N
100
concentration histograms, and (d)inN
30-50
concentration histograms
on summer and autumn months in some stations, leading to short periods of higher
concentrations in number concentrations of particle sizes smaller than 100 nm in
diameter.
In the histogram (occurrence) plots, the N
30-50
concentrations showed in some
stations weak seasonality, with wintertime concentrations more likely to have
decreased concentrations compared to summertime values. However, in the N
50
and N
100
concentrations, no seasonality was detected. The histograms are also
unimodal and relatively narrow, which suggests very homogenous environment for
all of the integrated number concentrations studied. There is also very little evidence
of a strong diurnal cycle in the aerosol sizes studied. The station annual median
concentrations of N
30-50
varied between 410 and 1,120 cm
3
,N
50
between 1,330 and
3,387 cm
3
with most stations over 2,300 cm
3
,andN
100
between 739 and
1,863 cm
3
. The lack of seasonality may have two major reasons. First of all, the
relative contribution of the natural aerosol particle sources is smaller than on more
remote stations, and secondly, the overall meteorological situation in Central Europe
has less strong influence on aerosol concentrations than, e.g., Northern Italy.
Overall, the results suggest that the particle number size distributions in Central
Europe are very similar over very large region, and even though the mean
concentrations somewhat vary from station to station, the background air in Europe
is homogenous from the aerosol point of view.
