1. Site selection Network and site representativeness Spatial clustering
Consistent sites selection for the selected period

2. Comparing EMEP model and obs. in light of population density
ES07
Representativity, NO2
IT01
NL91
BE32
AT02

3. network representativeness
Ideally one should have sites which represent the complete network since sites from different regions/emission influence may give different trends
How to make a representative selection
when unrepresentative number of sites in some regions?
when missing sites in regions?
Can use single sites representative i.e for LRT or downwind for specific sources (or source areas)
Use modells to fill the gaps

5. Trends in POPs at Zeppelin
gHCH
HCB
ppDDT
The declining levels of HCHs, DDTs, chlordanes, and PCBs in air are results of the international regulations on POPs.
After a declining trend in 1990s the levels of HCB have increased during the last 10 years. The reason has been suggested to depend on increased re-emissions from deposited HCB due to higher temperature and ice-free winters, or to a continuous use of pesticides containing HCB in some parts of the world
sum PCB
AMAP, Trends in Stockholm Convention Persistent Organic Pollutants (POPs) in Arctic Air, Human media and Biota. AMAP Technical Report to the Stockholm Convention. AMAP Technical Report No. 7 (2014),

6. Combine (all) available site
Tørseth et al 2012Atmos. Chem. Phys., 12, 5447–5481

7. Site clustrering Spatial to compare regions. Site characteristic.
E.g west/east/south/north or simiral
Site characteristic.
E.g Alpine/Arctic/urban/agricultural

8. (consistent) site selection for the selected period
Only use sites which have measurement the whole period?
Or possible to use all measurement available for the different years?
For some components there were less measurements before and a pity to not use the complete network in the present years
Howver is it possible to avoid bias in overall trend if not same sites for the selected period

10. Sulphate air concentration 2000-2010
Tørseth 2013
# 26
ALL EBAS
# 74

11. Total Nitrate, air concentration 2000-2010
Tørseth 2013
# 18
ALL EBAS
# 49

12. Benchmark dataset How to Identity sites suitable for trend analysis
Sites not influence by changes in surroundings
Sites/labs with satisfactory method, quality and completeness
Annual mean NO3 in precip
Lab perfermence in intercomparison

13. Global wet deposition of nss S from a global benchmark dataset
% change
Vet et al. A global assessment of precipitation chemistry and deposition Atmos. Env

14. Define criteria of which sites to use

15. Discussion topics Selection of sites Clustring techniques?
Dependent on what to study (region and representativity)
Dependent on which component and time period
Dependent on availability (completness) and quality
Clustring techniques?
National experts could identify which sites are suitable for trends
Post on a wiki page?
Identify sites where lab perform well in lab intercomparison and use recommended methods
Modellers could help assessing the suitability of the sites