ANNEX IX U.K.Criteria for determining the minimum number of sampling points for fixed measurement of concentrations of ozone

A. Minimum number of sampling points for fixed continuous measurements to assess compliance with target values, long-term objectives and information and alert thresholds where such measurements are the sole source of information U.K.

a At least 1 station in suburban areas, where the highest exposure of the population is likely to occur. In agglomerations at least 50 % of the stations shall be located in suburban areas.
b 1 station per 25 000 km2 for complex terrain is recommended.
Population (× 1 000)	Agglomerations (urban and suburban)a	Other zones (suburban and rural)a	Rural background
< 250		1	1 station/50 000 km2 as an average density over all zones per countryb
< 500	1	2
< 1 000	2	2
< 1 500	3	3
< 2 000	3	4
< 2 750	4	5
< 3 750	5	6
> 3 750	One additional station per 2 million inhabitants	One additional station per 2 million inhabitants

B. Minimum number of sampling points for fixed measurements for zones and agglomerations attaining the long-term objectives U.K.

The number of sampling points for ozone shall, in combination with other means of supplementary assessment such as air quality modelling and collocated nitrogen dioxide measurements, be sufficient to examine the trend of ozone pollution and check compliance with the long-term objectives. The number of stations located in agglomerations and other zones may be reduced to one-third of the number specified in Section A. Where information from fixed measurement stations is the sole source of information, at least one monitoring station shall be kept. If, in zones where there is supplementary assessment, the result of this is that a zone has no remaining station, coordination with the number of stations in neighbouring zones shall ensure adequate assessment of ozone concentrations against long-term objectives. The number of rural background stations shall be one per 100 000 km².