| Population (× 1,000) | Agglomerations (urban and suburban) (a) | Other zones (suburban and rural) (a) | Rural background |
|---|---|---|---|
(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 should be located in suburban areas. | |||
(b) 1 station per 25,000 km2 for complex terrain is recommended. | |||
| 0 – 250 | 1 | 1 station/50,000 km2 as an average density over all zones per country (b) | |
| 251 – 500 | 1 | 2 | |
| 501 – 1,000 | 2 | 2 | |
| 1,001 – 1,500 | 3 | 3 | |
| 1,501 – 2,000 | 3 | 4 | |
| 2,001 – 2,750 | 4 | 5 | |
| 2,751 – 3,750 | 5 | 6 | |
| >3,750 | 1 additional station per 2 million inhabitants | 1 additional station per 2 million inhabitants | |
The number of sampling points for ozone must, in combination with other means of supplementary assessment such as air quality modelling and co-located 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 Part I. Where information from fixed measurement stations is the sole source of information, at least one monitoring station should be kept. If, in zones where there is supplementary assessment, the result of this is that a zone has no remaining station, co-ordination with the number of stations in neighbouring zones must ensure adequate assessment of ozone concentrations against long-term objectives. The number of rural background stations should be 1 per 100,000 km2.