Results from the Swedish Urban measurement network have been used for comparison of measurement results from Tallinn. The two largest cities in Sweden, Stockholm, ca 1 million inhabitants, and Gothenburg, approximately 500 000 inhabitants, were used. The measurements within the urban network are made at only one sampling point in the centre of the city, which is located not to be directly influenced by traffic, for example in a square without vehicles. The closest classification would be as a B-site. The measurements are not directly comparable, neither as to number of sampling sites, nor as to measurement techniques and sampling intervals. Furthermore, the measurements within the Swedish Urban network are performed only during the winter months, October-March. The results do however give an indication of the pollution levels in the three cities.

In table 8 the results from the last two winter periods in Stockholm and Gothenburg are presented and compared to the results from the winter period measurement campaigns in Tallinn.

The most obvious difference, as expected, is in the incidences of higher SO₂ concentrations in Tallinn compared to in the Swedish cities. For NO₂ the levels are of the same order of magnitude.

Highest and lowest monthly average concentration (µg/m³) in Stockholm and Gothenburg during the two winter seasons, 1996-97 and 1997-98 as compared to winter results from B sites in Tallinn.

	Tallinn (B-sites) 34 sites	Stockholm 1 site	Gothenburg 1 site
NO2 (µg/m3)
Highest monthly mean	44	32	40
Lowest monthly mean	16	24	23
SO2 (µg/m3)
Highest monthly mean	16	3	4
Lowest monthly mean	1	1	1