Migration of traffic generated pollutants (PM2.5 and NO2) into a naturally-ventilated highrise slab block

Abstract

Increasing concerns on health issues caused by traffic-generated pollutants have led to the initiation of many new studies in this aspect. Especially in Singapore, where asthma is common among children, research on the dispersion of traffic pollutants in the tropics became more important. The purpose of this study is to quantify the traffic generated pollutant concentration levels at various heights of typical high-rise buildings located in close proximity to expressways. Hence, it includes the assessment of indoor/outdoor distribution profiles of PM2.5 and NO2. One naturally ventilated public housing building of slab block configuration was selected for this study. Three representative floors lower, mid and upper floors of the buildings were selected. Objective measurements, namely NO2 level, particle count, wind speed, ambient temperature and relative humidity were conducted at these selected floors. The results show that NO2 concentration was highest at the mid floors of the buildings when compared to the upper and lower floors in typical a day during the Northeast monsoon period. This could be due to the dense tree canopies planted alongside the expressway that deflected some of the traffic-polluted air from the lower levels towards the mid floors of the building as it traversed from the expressway towards the building. The tree canopies could have trapped also NO2. The upper floors had the least NO2 concentration due to dilution by the higher wind speed. Indoor/Outdoor Ratio was found to be less than 1 for all floors suggesting decrease in NO2 level from outdoor into the building. The difference between the vertical distribution profile of traffic generated pollutants need to be research further since this study in the tropics had shown a different vertical distribution profile for traffic generated NO2 concentration compared to those studies conducted in temperate climate, sub-tropical climate and dry climatic conditions. Thus, the microclimatic condition of the Singapore has to be scrutinized in detail.