AIR AND VENTILATION 1 POLLUTION
Substance benzene (C6H6 )
carbon monoxide (CO) formaldehyde (CH2
O) lead (Pb)
nitrogen dioxide (NO2 )
ozone (O3 particulate matter (PM2.5 sulphur dioxide (SO2 and PM10
polycyclic aromatic hydrocarbons )
) )
Guideline limit value by volume 5.0 g.m–3 10 mg.m–3 100 g.m–3 0.5 g.m–3 200 g.m–3 120 g.m–3 25 g.m–3 1 ng.m–3
(1 hour exposure) (PM10), 50 g.m–3 350 g.m–3 (PM10
(see original source) (1 hour exposure)
Selection of commonly quoted environmental pollutants – see original data source for full data: EC Air Quality Standards
http://ec.europa.eu/environment/air/quality/standards.htm
)
Inlet
Single prevailing wind
Inlet
Two prevailing winds
Figure 1: Position of intake relative to exhaust as a function of prevailing winds (Source: CIBSE TM21)
motor vehicles and the level of solar radiation. There will also be some delay in the reaction between the NO2 and the sunlight. This reaction time could well account for
the findings reported in TM21 indicating that ozone levels at roof level exceed those at street level in research undertaken by BSRIA (Location of ventilation air intakes 1996). This is due to the delay on the production of ozone as the NO2 diffuses from its original tailpipe location. Ozone is particularly important in the
assessment of indoor air quality, due to its secondary impact when it reacts with certain organic compounds inside the building to produce short-lived products that adversely affect human health. The pollutants that are included in the
There are several methods for determining the expected levels of pollutants in the outside air
particulate category cover a very wide range of sizes and sources, ranging from agricultural and horticultural dusts to industrial process and vehicle emissions. There is increasing concern about the health effects of the smaller range designated PM2.5 that can particularly result from diesel emissions and biomass
boilers. The table (left) provides a subset of the pollutants that are considered relevant in the assessment of air quality. As suggested by BRE in Ventilation for healthy buildings – reducing the impact of urban air pollution, the local environmental health department should be consulted to determine whether monitoring has already been carried out at a location with a similar environment close to the site under consideration. It would be prudent to ensure that the quality of a building’s incoming air meets at least the UK Air Quality Standard Regulations 2010. These refer to the EC Directive 2008/50/EC on ambient air quality, which sets limits for concentrations of principal air pollutants in outdoor air. There are a number of methods for
determining the expected levels of pollutants in outdoor air that will account for regional, district and local pollution sources. BRE Trust’s Ventilation for Healthy Buildings guidance includes a methodology for the prediction of external air quality. It considers a building’s location and its relation to the immediate surroundings, structures and local topography, and the contributing sources of pollutants from long-, intermediate- and short-range distances. As well as considering the effect of
local industrial and background pollution, CIBSE TM21 also provides a method to estimate the expected emissions from local traffic. However, as resources and data sources allow, this may be more effectively assessed through the use of computational fluid dynamics (CFD) analysis. TM21 shows that increased carbon monoxide (CO) concentrations from major roads will reduce to imperceptible levels at a distance of 200m. The impact of local traffic pollution on the internal
48
CIBSE Journal March 2012
www.cibsejournal.com
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