Indoor exposure to outdoor air pollutants controlled by different urban design strategies

摘要

Background: In compact mega-cities such as London and Beijing, motor vehicle emissions have been a major source of local urban pollutions especially from the urban viaduct. However, a significant part of exposure to outdoor pollution occurs indoors as people spend over 80% of their time living indoors and the outdoor pollutants can penetrate indoors. Urban design can affect the outdoor air pollution as well as indoor-outdoor exchange, and therefore indoor exposure, however, little research has quantified such impact. Aim: The aim of this paper is to investigate the impact of urban design strategies on the indoor exposure to outdoor traffic pollutants for different age-groups of population. Methods: Coupling indoor and outdoor Computational fluid dynamic (CFD) model is used to simulate the airflow and pollution dispersion between the street canyon and building interior space. Building intake fraction was introduced to evaluate the accumulated intake fraction indoors from the outdoor mobile vehicle emission. Results: Our studies provide new insights on how to reduce indoor exposure to outdoor origins by improving outdoor urban design rather than focusing on building design itself. Detailed results drawn from this study show: 1) When the aspect ratio equals 1, indoor personal exposure to street pollution will be reduced if the single pollutant source is elevated by the viaduct; 2) High upstream velocity can depress the pollutant concentration. Pollutant dispersion can be stronger by great ground heating intensity under same upstream velocity; 3) The indoor exposure to street pollution can be lessened when broadening the street under the condition of same building height and source strength; 4) Personal intake fraction ranges from 1500 to 6500 ppm depending on the different urban canyon and building design.