Comparison of outdoor and indoor mobile source-related volatile organic compounds between low- and high-floor apartments

The current study examined the hypothesis that there may be vertical variation in mobile source-related volatile organic compound (VOC) concentrations in high-rise apartment buildings. One hundred twelve homes in 56 high-rise apartment buildings with 10 or more stories participated in the study. Both the outdoor and the indoor air concentrations of three VOCs [methyl-tertiary butyl ether (MTBE), benzene, and toluene] were significantly higher for the low-floor apartments than for the high-floor apartments (P<0.05). The median outdoor concentrations were 5.4, 6.8, and 29.1 μg/m3, respectively, for the low-floor apartments, yet 4.4, 4.3, and 21.9 μg/m3, respectively, for the high-floor apartments. Meanwhile, the median indoor concentrations were 6.3, 9.4, and 44.8 μg/m3, respectively, for the low-floor apartments, yet 5.1, 7.6, and 38.8 μg/m3, respectively, for the high-floor apartments. These findings indicate that residents of low-floor apartments are exposed to elevated residential levels of mobile source-related VOCs compared to high-floor apartment residents. The indoor concentrations of the target VOCs, except for MTBE, were significantly higher than the outdoor air concentrations for both the low and high floors (P<0.05). Plus, the outdoor and indoor VOC concentrations were significantly different between the daytime and nighttime data sets for both low- and high-floor apartments, with a P value of less than or close to 0.05.