Particulate-bound polycyclic aromatic hydrocarbons in naturally ventilated multi-storey residential buildings of Singapore: Vertical distribution and potential health risks

Abstract

The main objective of the study is to quantify the polycyclic aromatic hydrocarbons (PAHs) concentration levels (US EPA priority components) in fine traffic-generated particles (PM 2.5) at various heights of typical multi-storey public housing buildings located in close proximity, i.e. within 30 m and along a busy major expressway in Singapore. The secondary objective is to estimate the potential health risks associated with inhalation exposure, based on the toxic equivalency factors (TEFs) at the various floors of these buildings. Two typical public housing buildings, both naturally ventilated residential apartment blocks, of point block configuration (22-storey) and slab block configuration (16-storey) were selected for the study. Particulate samples were collected for chemical analysis at three representative floors: the lower, the mid, and the upper floors of the buildings. Key meteorological parameters such as wind speed, wind direction, ambient temperature, and relative humidity were also measured at the representative floors. All samples were analyzed for the 16 PAH priority pollutants listed by US EPA. The vertical PAH distribution profile varies with height of building depending on the type of block configuration. The total mean concentrations of particulate PAHs for point and slab blocks are 3.32±1.76 ng/m 3 (0.56–7.2 ng/m 3) and 6.0±1.88 ng/m 3 (3.19–10.26 ng/m 3), respectively. For the point block, the highest mean total PAH concentration occurred at the mid floor followed by the upper floor. The lower floor had the least mean total PAH concentration. For the slab block, the highest mean total PAH concentration occurred at the lower floor and remained almost constant up to the mid floor and thereafter gradually decreased from mid floor to upper floor of the building. These results suggest that the building configuration influences the vertical distribution of particulate PAHs. The dominant particulate PAHs measured at the point block are naphthalene, acenaphthylene, benzo( b)fluoranthene, and benzo( g, h, i)perylene while those for the slab block, the main particulate PAHs are naphthalene, phenanthrene, fluoranthene, and benzo( g, h, i)perylene. The Bpe/Ind ratio for both blocks ranged from 0.92±0.2 to 1.63±0.6 indicating particulate PAHs are contributed by a mixture of both diesel and petrol engine type of vehicles, with diesel engine vehicles contributing a higher percentage of particulate PAHs to the different floor levels of both buildings. The total BaP eq concentrations for point and slab blocks are 1.06±0.64 ng/m 3 (0.14–2.45 ng/m 3) and 0.94±1.22 ng/m 3 (0.10–4.59 ng/m 3), respectively. The total BaP equivalency results showed the potential health risk to cancer due to inhalation exposure is of concern for residents living in both blocks since the total BaP eq concentrations for both blocks were very close to, or slightly exceeded the maximum permissible risk level of 1 ng/m 3 of benzo( a)pyrene.