Internal contamination from outdoor pollution sources and ventilation intake placement

Internal contamination of buildings from outdoor pollution sources therefore depends upon the pollutant sources, the physical characteristics of the building and its relation to its surroundings, the ventilation strategy employed and the location of the air intake. Whatever type of ventilation system is used, it is essential to ensure that the intake air is not contaminated. This is especially important in DOENI air quality management areas (AQMA) where, by definition, pollution levels of at least one pollutant are already close to the air quality standards. Table D1 Guidance on ventilation intake placement for minimising ingress of pollutants: Local static sources (Parking areas, Welding areas, Loading bays, Adjacent building exhausts, Stack discharges): Ventilation intakes need to be placed away from the direct impact of short-range pollution sources especially if the sources are within a few metres of the building. Some guidance is given in CIBSE TM21. Urban traffic: Air intakes for buildings positioned directly adjacent to urban roads should be as high as possible and away from the direct influence of the source so as to minimise the ingress of traffic pollutants. There will be exceptions to this simple guide and these risks may need to be measured by modelling. In such cases, it is recommended that expert advice is sought. For buildings located one or two streets away, the placement of intakes is less critical. Building features/layout (Courtyards, Street canyons): Intakes should not be located in these spaces where there are air pollutant discharges. This includes emission discharges from building ventilation system exhausts. If air intakes are to be located in these spaces, they should be positioned as far as possible from the source in an open or well-ventilated area. In addition, steps should be taken to reduce the polluted source (e.g. parking and loading should be avoided as pollutants can accumulate in enclosed regions such as courtyards). Multiple sources: Where there are a large number of local sources, the combined effect of these around the façade of the building should be measured. The façade experiencing the lowest concentration of the pollutants would be an obvious choice for locating ventilation intakes but this will require expert assistance such as numerical and wind tunnel modelling. In general, however, it is recommended that the air intakes be positioned as far from the source at a location where air is free to move around the intake. Weather factors: In areas where predominant wind comes from opposing directions (e.g. a valley location) the air intakes and outlets should point in opposite directions. In complex urban layouts, complex wind flows are likely to occur. In these cases, expert advice should be sought.