Office of Public Sector Information
SCHEDULE 4 continued PART 2
| Upper assessment threshold | 60% of target value (3.6 ng/m3) |
| Lower assessment threshold | 40% of target value (2.4 ng/m3) |
| Upper assessment threshold | 60% of target value (0.6 ng/m3) |
| Lower assessment threshold | 40% of target value (0.4 ng/m3) |
| Upper assessment threshold | 60% of target value (3 ng/m3) |
| Lower assessment threshold | 40% of target value (2 ng/m3) |
| Upper assessment threshold | 70% of target value (14 ng/m3) |
| Lower assessment threshold | 50% of target value (10 ng/m3) |
1. The representative concentration of the relevant pollutant shall be determined on the basis of concentrations during the previous five years where sufficient data are available. The upper assessment threshold will be deemed to have been exceeded if it has been exceeded during at least three separate years out of the previous five years. Similarly, the lower assessment threshold will be deemed to have been equalled or exceeded if it has been equally or exceeded during at least three separate years out of the previous five years.
2. Where fewer than five years’ data are available, measurement campaigns of short duration during the period of the year and at locations likely to be typical of the highest concentrations may be combined with results obtained from emission inventories and modelling to determine exceedances of the upper and lower assessment thresholds.
Regulation 15(1), (4) and (5)
1. This Part sets out the minimum number of sampling points for fixed measurement of Group A pollutants to assess compliance with limit values for the protection of human health and alert thresholds in zones where fixed measurement is the sole source of information.
(1)
For NO2 and PM10 to include at least one urban-background station and one traffic-orientated station; this requirement shall also apply to benzene and carbon monoxide provided that it does not increase the number of sampling points. |
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| Population of zone (thousands) | Where concentrations exceed the upper assessment threshold(1) | Where maximum concentrations are between the upper and lower assessment thresholds | For nitrogen dioxide and sulphur dioxide in agglomerations where maximum concentrations are below the lower assessment thresholds |
|---|---|---|---|
| 0–249 | 1 | 1 | 1 |
| 250–499 | 2 | 1 | 1 |
| 500–749 | 2 | 1 | 1 |
| 750–999 | 3 | 1 | 1 |
| 1,000–1,499 | 4 | 2 | 1 |
| 1,500–1,999 | 5 | 2 | 1 |
| 2,000–2,749 | 6 | 3 | 2 |
| 2,750–3,749 | 7 | 3 | 2 |
| 3,750–4,749 | 8 | 4 | 2 |
| 4,750–5,999 | 9 | 4 | 2 |
| 6,000 or more | 10 | 5 | 3 |
2. For the assessment of pollution in the vicinity of point sources, the number of sampling points for fixed measurement shall be calculated taking into account emission densities, the likely distribution patterns of ambient-air pollution and the potential exposure of the population.
The Air Quality Standards Regulations 2007