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INTRODUCTION

Outdoor air pollution is one of the major environmental problems today. It is associated with a broad spectrum of acute and chronic health effects (e.g. Brunekreef and Holgate 2002). The pollutants that are brought into the atmosphere by various sources are dispersed (advected and diffused) over a wide range of horizontal length scales (L). Dispersion within the urban environment (L < 5 km / 3.1 miles) is referred to as microscale dispersion. Important parameters for microscale dispersion are building geometry and environment topography, wind speed, wind direction, turbulence, stability, temperature, humidity and solar radiation.

In the built environment, both the outdoor exposure of pedestrians and the indoor exposure of building inhabitants are of concern (Fig. 1). Outdoor and indoor air pollution are a main concern of building and air-conditioning engineers that design the ventilation inlets and outlets on building facades or roofs (Drivas and Shair 1974, ASHRAE 1999). Indoor air pollution by outdoor air pollutants can be caused by the reingestion of the contaminated exhaust air by the same building or by the intake of exhaust from other sources such as nearby buildings, street traffic, vehicle parking lots and loading docks, emergency generators and cooling towers (Smeaton et al. 1991, Meroney 2008).