Chemistry Reference
In-Depth Information
Fig. 5 Britain and Ireland aerosol overview (location shown in the
inset
). (a) Histograms of N
100
concentration in both stations, (b) Mace Head size distributions, showing 16th, median (
thick line
),
and 83rd percentiles of size distribution functions
influencing the size distributions. Although the similarities between the stations are
not as obvious as in Central Europe, the datasets have uniformity in regard to
seasonal and size distribution behavior. The winter number concentrations are
usually lowest, especially for smaller (diameter less than 100 nm) particle sizes.
The seasonality also affects the observed differences of day- and night-time values
due to differing length of day in the northern latitudes. All of the stations showed
bimodal median particle number size distributions, with clear Aitken and accumu-
lation modes. The concentration distributions on some stations show multiple
modes, suggesting a combination of more polluted air masses and cleaner air
from the Arctic or Atlantic oceans.
The CCN-sized particle number concentration histograms of the Nordic stations
are similar for both N
50
and N
100
. The stations in general had greater concentrations
in summertime, although the concentrations were also elevated during spring in
some stations. Northernmost Pallas station concentrations have a very wide histo-
gram, especially in wintertime, suggesting a wide range of sources affecting the
concentrations observed at the station. The seasonal variations in CCN-sized
particles are large at almost all Nordic stations.
3.2.4 Britain and Ireland Background (See Fig.
5
)
The two EUSAAR/ACTRIS stations in the Britain and Irish stations show not only a
significant inter-station variability, but also many similarities. The stations have high
seasonal variation and large variance in intra-seasonal concentrations. The station
data show a prominent spring-summer maximum in all sizes from 30 to 70 nm. The
variability was probably due to occurrences of both clean Atlantic and polluted local
air masses, and the maximum value at Mace Head during summer months can be
attributed to enchanted marine biota activity, which increases the sub-micron particle
mass concentration of non-seasalt sulfate and organic aerosol [
21
].
