The Air Quality Limit Values Regulations 2003

Regulation 9(4), (6), (7), (9), (11)

SCHEDULE 5 CRITERIA FOR DETERMINING MINIMUM NUMBERS OF SAMPLING POINTS FOR FIXED MEASUREMENT OF CONCENTRATIONS OF RELEVANT POLLUTANTS AND OZONE IN AMBIENT AIR

PART I Relevant pollutants: minimum number of sampling points for fixed measurement 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

(a) Diffuse sources

Population of zone (thousands )	If concentrations exceed the upper assessment threshold	If maximum concentrations are between the upper and lower assessment thresholds	For SO2 and NO2 in agglomerations where maximum concentrations are below the lower assessment thresholds
0-250	1	1	not applicable
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	10	5	3
	For NO2 and particulate matter: 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

(b) Point sources

For the assessment of pollution in the vicinity of point sources, the number of sampling points for fixed measurement should be calculated taking into account emission densities, the likely distribution patterns of ambient-air pollution and the potential exposure of the population.

PART II Relevant pollutants: minimum number of sampling points for fixed measurements to assess compliance with limit values for the protection of ecosystems or vegetation in zones other than agglomerations

If maximum concentrations exceed the upper assessment threshold	If maximum concentrations are between the upper and lower assessment thresholds
1 station every 20,000 km2	1 station every 40,000 km2

In island zones the number of sampling points for fixed measurement should be calculated taking into account the likely distribution patterns of ambient-air pollution and the potential exposure of ecosystems or vegetation.

PART III Ozone: minimum number of sampling points for fixed continuous measurement to assess air quality in view of compliance with the target values, long-term objectives and information and alert thresholds where continuous measurement is the sole source of information

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 in England (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

PART IV Ozone: minimum number of sampling points for fixed measurements for zones attaining the long-term objectives

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 III. 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.