ANNEX IIIAssessment of ambient air quality and location of sampling points for the measurement of sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter (PM10 and PM2,5), lead, benzene and carbon monoxide in ambient air
C.Microscale siting of sampling points
In so far as is practicable, the following shall apply:
the flow around the inlet sampling probe shall be unrestricted (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 and at least 0,5 m from the nearest building in the case of sampling points representing air quality at the building line),
in general, the inlet sampling point shall 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. Higher siting may also be appropriate if the station is representative of a large area,
the inlet probe shall not be positioned in the immediate vicinity of sources in order to avoid the direct intake of emissions unmixed with ambient air,
the sampler's exhaust outlet shall be positioned so that recirculation of exhaust air to the sampler inlet is avoided,
for all pollutants, traffic-orientated sampling probes shall be at least 25 m from the edge of major junctions and no more than 10 m from the kerbside.,
The following factors may also be taken into account:
interfering sources,
security,
access,
availability of electrical power and telephone communications,
visibility of the site in relation to its surroundings,
safety of the public and operators,
the desirability of co-locating sampling points for different pollutants,
planning requirements.,