Chemistry Reference
In-Depth Information
100
90
80
70
60
50
-10
0
10
20
30
Longitude, degrees E
Fig. 3 Decadal average maximum 8-h mean ozone levels along a west-east transect through
central Europe
values to the north in Scandinavia. These tendencies are consistent with the concept
of an “ozone maximum region” developed above.
Figure
3
constructs a west-east transect through Europe using the stations with
latitudes in the range 45
-55
N and also excluding the CH0001G station. The
points appear to fall within a curved area with a maximum in the 5
-10
E range,
falling off to lower values on either side of the maximum towards the fringes of
Europe. Again, this is consistent with the concept of an “ozone maximum region”.
3 Trends in Episodic Peak Ozone Levels Across Europe
over the 1980-2009 Period
A clear-cut feature of the EMEP 8-h maximum ozone database is the presence of
apparent trends. There is a tendency for the highest recorded values to be found in
the early years and for the lowest values in the latest years. The aim of this section is
to quantify any trends and to offer explanations as to their origins. Trend analysis is
not straightforward in the case of the EMEP 8-h maximum ozone database because
of a number of difficulties. The first difficulty is the marked year-on-year variability
found in the time series data for the individual stations. The second difficulty arises
from the presence of gaps in the datasets which result from the strict criteria that
have been applied in this analysis based on data capture. Finally, the number of
stations operating in a given year has changed markedly through the 1980-2009
period as interest in ground-level ozone has developed. The approach adopted has
