Assessment of the air quality in indoor car parks

A comparative survey of indoor and outdoor air quality (AQ) for an enclosed (GL1) and a semi-enclosed (UST1) car park in Hong Kong was conducted from August to December 2000. Seventy-two canister samples were collected and analysed for one hundred C₃-C₁₂ by gas chromatography/mass spectrometry. Carbon monoxide (CO), carbon dioxide, temperature, relative humidity and particulate matter were also measured. The CO levels at GL1 complied with local AQ objectives for Indoor Car Parks and ASHRAE guidelines, but were more than double those of the outdoor air. The PM₁₀ and PM_2.5 concentrations were also found to be higher in the indoor environments. High mass fractions of aliphatic and aromatic compounds detected at GL1 showed that fuel evaporation and motor vehicular exhaust were the major contributors to the VOCs. In addition, the number and abundance of VOC species were higher in the enclosed environment than outdoors. The high indoor/outdoor (I/O) AQ ratios and poor I/O correlations at GL sites showed that the existing ventilation system at the site was inefficient. Enclosed car parks with their intrinsic source emissions are unlike other indoor public places. The CO and VOC pollution coupled with insufficient ventilation, as in this study, make them potentially hazardous to users. The composition of gasoline on sale locally was studied to shed light on the VOC composition in the car park environments. In addition, the sources of isoprene in the enclosed car parks were explored in a correlation study.