Chemistry Reference
In-Depth Information
Table 2 Trend analysis for the five long-running EMEP monitoring stations over the 1980-2009
period, showing the Sen's slope estimates, initial 1980 levels and significance levels
Station
Slope, ppb per year
Initial 1980 level, ppb
Significance level
GB0039R
1.4
0.9
118
a
¼
0.01
GB0036R
1.2
0.7
109
a
¼
0.01
DE0003R
0.0
95
a
>
0.1
DE0002R
0.2
89
a
>
0.1
DE0001R
0.1
81
a
>
0.1
Notes: the confidence limits on the Sen's slope estimates are shown as 2-
intervals
s
therefore been to split the 1980-2009 period into sub-periods with consistent and
homogeneous sets of stations in each.
Table
2
summarises the available trend data for the complete 1980-2009 period
at the five longest-running stations in the EMEP 8-h maximum ozone database.
Application of the Mann-Kendall test [
22
] confirmed that all five stations exhibited
downwards trends. The two United Kingdom stations: GB0039R Sibton and
GB0036R Harwell, the latter in the south east of England, showed highly statisti-
cally significant downwards trends at the
0.01 level of significance. The Sen's
slope estimates [
22
] were
1.4
0.9 ppb per year and
1.2
0.7 ppb per year,
respectively. The downwards trends at the three German stations: DE0003R,
DE0002R and DE0001R were not highly significant and showed a significance
level which was greater than 0.1. It appears that the downwards trends were greater
for the stations with the higher initial annual 8-h maximum ozone levels
extrapolated back to 1980. For the stations with the lower annual 8-h maximum
ozone levels, no highly statistically significant trends were apparent.
Table
3
summarises the trends found for the 1990-2009 period ranked in
descending order of their annual values extrapolated back to 1990 using the trend
analysis. Of the 40 stations analysed using the Mann-Kendall test [
22
], 16 stations
showed highly statistically significant (
a
¼
0.1) downwards trends, 19 stations
showed downwards trends that were not high statistically significant (
a
0.1)
and 5 showed no or slightly positive trends that, again, were not highly statistically
significant (
a
>
0.1). The Sen's slope estimates [
22
] revealed that the highest
downwards trend of
a
>
1.1 ppb per year was exhibited by the IT0004R Ispra
station, the station with the highest initial 1990 value. Eleven stations showed
highly statistically significant (
2.3
1 ppb
per year, in addition to the Montelibretti station: GB0013R Yarner Wood,
GB0038R Lullington Heath, NL0010R Vredepeel, GB0036R Harwell, GB0031R
Aston Hill, AT0002R Vorhegg, SE0011R Vavihill, GB0002R Eskdalemuir,
NO0001R Birkenes and GB0006R Lough Navar. There was a clear tendency for
the stations with the largest annual values extrapolated back to 1990 to show the
largest downwards trends.
Table
4
summarises the trends found for the somewhat shorter period from 1993
to 2009, ranked in order of their annual values extrapolated back to 1990 using the
trend analyses. Of the 29 stations analysed, the Mann-Kendall test [
22
] showed that
7 stations exhibited highly statistically significant (
a
0.1) downwards trends that exceeded
a
0.1) downwards trends,
