Chemistry Reference
In-Depth Information
Table 5 Trend analysis for the nine EMEP monitoring stations over the 2000-2009 period that
exhibited highly statistically significant downwards trends
Station
Slope, ppb per year
Initial 2000 level, ppb
Significance level
CH0003R
1.6
1.4
101
15
a
¼
0.1
GB0002R
2.4
2.4
100
11
a
¼
0.05
FR0014R
1.9
1.9
97
14
a
¼
0.1
AT0047R
0.7
0.9
95
8
a
¼
0.1
DE0002R
2.0
1.7
95
10
a
¼
0.1
AT0043R
1.3
1.3
92
11
a
¼
0.05
CH0001G
1.7
1.3
91
8
a
¼
0.01
ES0010R
2.1
1.6
90
6
a
¼
0.1
DK0041R
1.3
1.4
90
7
a
¼
0.1
AT0032R
0.6
0.8
87
6
a
¼
0.1
BE0035R
1.0
1.0
82
13
a
¼
0.05
BE0001R
1.0
0.7
81
5
a
¼
0.05
NL0009R
0.9
1.0
75
6
a
¼
0.1
Notes
: the confidence limits on the Sen's slope estimates are shown as 2-
intervals
s
2.4 ppb per year was GB0002R Eskdalemuir. Altogether, all but 3 of the
13 stations in Table
5
showed downwards trends that were greater than 1 ppb per
year. The stations that showed the largest downwards trends were AT0043R
Forsthof, BE0001R Offagne, BE0035R Vezin, CH0001G Jungfraujoch,
CH0003R Tanikon, DE0002R Langenbrugge, DK0041R Lille Valby, ES0010R
Cabo de Creus and FR0014R Montandon, in addition to GB0002R Eskdalemuir.
2.4
4 Why Are the Downwards Trends Largest for the Stations
with the Highest Episodic Peak Levels?
In summarising the observed trends in episodic peak ozone levels over the
1980-2009 period, a clear tendency has emerged for those stations with the highest
episodic peak levels to show the largest downwards trends. To attempt to illustrate
this apparent tendency, a scatter plot has been constructed, see Fig.
4
, with the trend
data over the 1990-2009 and 1993-2009 sub-periods, taken from Tables
3
and
4
.
In this scatter plot, a point is plotted for each station, showing along the
x
-axis, the
annual maximum 8-h ozone maximum at the start of the trend analysis in 1990, and
along the
y
-axis, the Sen's slope estimates [
22
] from the trend analysis. The plotted
points are shown larger for those stations where the Mann-Kendall tests [
22
] were
highly statistically significant (
a
0.1) and smaller where the trends were not
highly statistically significant (
0.1). The scatter plot shows that, indeed, the
downwards trends were larger for the stations with higher episodic peak ozone
levels and smaller for the least exposed stations.
These episodic peak ozone levels have unquestionably responded to European air
quality policy initiatives that have secured reductions in man-made NO
x
and VOC
a
>
