Air pollution characteristics and human health risk assessment of underground parking garages in Xi'an, China

Due to the rapid increase of population density and automobile vehicle numbers in mega-cities, large underground garages have become universal supporting facilities to meet the demand for parking spaces in the recently-built commercial complexes and high-rise residential communities. Natural ventilation was insufficient to discharge vehicle-induced pollutants out of the enclosed underground spaces, which could pose a potential threat to people's health. This study aims to determine the spatial and temporal distribution characteristics of pollutants concentration and the health risk of underground parking garages (UPGs)' staff and users. Field measurements were conducted on the air pollutants concentrations and the users' exposure characteristics in 11 commercial UPGs and three high-rise residential UPGs with natural ventilation in Xi'an. The pollutants concentrations were higher in the afternoon and morning of commercial and high-rise residential UPGs. In general, the particulate matters (PM2.5 and PM10), HCHO, TVOC and BTEX (benzene, toluene, ethylbenzene and xylenes) concentrations in commercial and residential UPGs were 0.069/0.067 mg/m(3), 0.12/0.097 mg/m(3), 0.014/0.017 mg/m(3), 1.8/1.8 mg/m(3), 0.056/0.10 mg/m(3), 0.19/0.29 mg/m(3) and 0.41/0.49 mg/m(3), respectively. TVOC and BTEX concentrations in UPGs significantly correlated with traffic volume (p < 0.01). In different groups, the entropy values of carcinogenic and non-carcinogenic risks were: staffs > children travelling with adults > adults. In particular, occupational long-term (employee) exposure could lead to both carcinogenic and non-carcinogenic risks.