Site environment types
Descriptions of the environment type classifications used for classifying air quality monitoring sites are shown below:
Urban area (U)
Continuously built-up urban area meaning complete (or at least highly predominant) building-up of the street front side by buildings with at least two floors or large detached buildings with at least two floors. With the exception of city parks, the built-up area is not mixed with non-urbanised areas. For the measurement of ozone, the urban area is defined as locations such as residential and commercial areas of cities, parks (away from the trees), big streets or squares with very little or no traffic, open areas characteristic of educational, sports or recreation facilities. Urban sites should measure air quality which is representative of a few km2.
Suburban area (S)
Largely built-up urban area. ‘Largely built-up’ means contiguous settlement of detached buildings of any size with a building density less than for ‘continuously built-up’ area. The built-up area is mixed with non-urbanised areas (e.g. agricultural, lakes, woods). It must also be noted that ‘suburban’ as defined here has a different meaning than in every day English i.e. ‘an outlying part of a city or town’ suggesting that a suburban area is always associated to an urban area. In our context, a suburban area can be suburban on its own without any urban part. For the measurement of ozone, suburban areas include where population, sensitive crops or natural ecosystems located in the outer fringe of an agglomeration are exposed to high ozone levels. Suburban sites should measure air quality which is representative of some tens of km2.
Rural area (R)
Sampling points targeted at the protection of vegetation and natural ecosystems shall be sited more than 20 km away from agglomerations and more than 5 km away from other built-up areas, industrial installations or motorways or major roads, so that the air sampled is representative of air quality in a surrounding area of at least 1 000 km2. Stations can be located in small settlements and/or areas with natural ecosystems, forests or crops.
At all site types, the flow around the inlet sampling probe shall be unrestricted (free in an arc of at least 270°) and at least 50cm away from buildings and trees. The inlet sampling point shall normally be between 1.5 m and 4 m above the ground, in the breathing zone, and shall not be positioned in the immediate vicinity of sources.
In accordance with Directive 2008/50/EC, air quality need not be assessed at any locations situated within areas where members of the public do not have access and there is no fixed habitation. This includes factory premises and industrial installations where health and safety at work regulations apply. It also includes the carriageway and central reservations of roads except where there is normally pedestrian access to the central reservation.
Traffic station (T)
Located such that its pollution level is determined predominantly by the emissions from nearby traffic (roads, motorways, highways). Air sampled at traffic sites must be representative of air quality for a street segment no less than 100 m length. Sampling probes shall be at least 25 m from the edge of major junctions and no more than 10 m from the kerbside.
Industrial station (I)
Located such that its pollution level is influenced predominantly by emissions from nearby single industrial sources or industrial areas with many sources. Industry source is here taken in its wide meaning including sources like power generation, incinerators and waste treatment plants. Air sampled at industrial sites must be representative of air quality for an area of at least 250 m × 250 m. The sampling point shall be installed downwind of the source in the nearest residential area.
Background station (B)
Located such that its pollution level is not influenced significantly by any single source or street, but rather by the integrated contribution from all sources upwind of the station e.g. by all traffic, combustion sources etc. upwind of the station in a city, or by all upwind source areas (cities, industrial areas) in a rural area. These sampling points shall, as a general rule, be representative for several square kilometres. At rural background sites, the sampling point should not be influenced by agglomerations or industrial sites in its vicinity, i.e. sites closer than five kilometres.