Chemistry Reference
In-Depth Information
Fig. 4 Key features of submicron aerosol measured at North European EUSAAR stations.
(a) location of the stations, (b) histograms of the annual N
30-50
concentrations, (c) seasonal
median size distributions, and (d) seasonal N
100
variation at Hyyti¨l¨, Finland
3.2.2 Polluted Northern Italian Background (See Fig.
3
)
An extreme case of polluted background station was the Joint Research Centre
station near Ispra in Northern Italy. Although the N
30-50
concentrations were
similar to Central European stations, the concentration levels in the larger submi-
cron particle sizes were significantly higher, with median N
50
concentration of
4,448 cm
3
. The seasonality of N
50
and N
100
particles was also very high, with
wintertime median N
100
concentrations approaching 10,000 cm
3
. The station was
characterized by a strong anthropogenic influence and wintertime inversions, which
trapped the pollution near the surface. These effects lead to extreme episodes with
high concentrations in accumulation mode.
3.2.3 North European Background (See Fig.
4
)
Northern Europe is characterized by strong seasonal variation in particle number
size distributions and much lower overall concentrations than Central Europe. The
high seasonality is from a far larger fraction of non-anthropogenic sources
