PART 4 Microscale siting

14.  The following guidelines should be met as far as practicable—

(a) the flow around the inlet sampling probe should be unrestricted (and, for ozone sampling, free in an arc of at least 270°), without any obstructions affecting the airflow in the vicinity of the sampler (normally some metres away from buildings, balconies, trees and other obstacles by more than twice the height the obstacle protrudes above the sampler and at least 0.5 m from the nearest building in the case of sampling points representing air quality at the building line);

(b) in general, the inlet sampling point should be between 1.5 m (the breathing zone) and 4 m above the ground. Higher positions (up to 8 m) may be necessary in some circumstances and in wooded areas. Higher siting may also be appropriate if the station is representative of a large area;

(c) the inlet probe should not be positioned in the immediate vicinity of sources in order to avoid the direct intake of emissions unmixed with ambient air;

(d) the sampler’s exhaust outlet should be positioned so that recirculation of exhaust air to the sampler inlet is avoided;

(e) in relation to the location of traffic orientated samplers—

(i) for all pollutants, such sampling points should be at least 25 m from the edge of major junctions and at least 4 m from the centre of the nearest traffic lane,

(ii) for nitrogen dioxide and carbon monoxide, inlets should be no more than 5 m from the kerbside, and

(iii) for PM₁₀, lead, benzene and Group B pollutants, inlets should be sited so as to be representative of air quality near to the building line;

(f) for ozone, the inlet probe should be positioned well away from such sources as furnaces and incineration flues and more than 10 m from the nearest road, with distance increasing as a function of traffic intensity;

(g) for deposition measurements in rural background areas as respects Group B pollutants and other pollutants falling within regulations 19 and 20, the European Monitoring and Evaluation of Pollutants guidelines and criteria should be applied as far as practicable.

15.  The following factors may also be taken into account—

(a) interfering sources;

(b) security;

(c) access;

(d) availability of electrical power and telephone communications;

(e) visibility of the site in relation to its surroundings;

(f) safety of public and operators;

(g) the desirability of co-locating sampling points for different pollutants;

(h) planning requirements.

PART 5

Documentation and review of site selection

16.  The site-selection procedures should be fully documented at the classification stage by such means as compass-point photographs of the surrounding area and a detailed map. Sites should be reviewed at regular intervals with repeated documentation to ensure that selection criteria remain valid over time.

17.  For ozone, this requires screening and interpretation of the monitoring data in the context of the meteorological and photochemical processes affecting the ozone concentrations measured at the respective site.

Regulation 15(2)

SCHEDULE 6 Minimum number of sampling points

PART 1 Group A pollutants: human health-based limit values and alert thresholds

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.

Diffuse sources

Point sources

2.  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.