In so far as is practicable, the following shall apply:

• F1the flow around the inlet sampling probe shall be unrestricted (in general free in an arc of at least 270° or 180° for sampling points at the building line) without any obstructions affecting the airflow in the vicinity of the inlet (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 siting may also be appropriate if the station is representative of a large area and any derogations should be fully documented,

• 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,

• F1for 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. A ‘major junction’ to be considered here is a junction which interrupts the traffic flow and causes different emissions (stop&go) from the rest of the road.,

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.,

F2Any deviation from the criteria listed in this Section shall be fully documented through the procedures described in Section D.