Exposure to phthalates has recently become a major public health concern. The information of indoor airborne phthalates and their air-particle partition in real indoor environmental condition is still limited. In this study, the gas- and PM-concentrations of 7 phthalates in 40 residences were concurrently measured in summer and winter. The major phthalates (median concentration in the summer and winter, respectively) in indoor air were DMP (2442.3 and 2403.4 ng/m), DiBP (801.0 and 640.0 ng/m) and DnBP (5173.2 and 1379.6 ng/m), whereas the major phthalates in PM were DiBP (1055.1 and 585.9 ng/m) and DnBP (1658.5 and 1517.0 ng/m) and DEHP (215.1 and 344.9 ng/m). Air-PM partition coefficients (K) of DiBP, DnBP and DEHP were calculated: the summer and winter median values (m/μg) were 0.053 and 0.011 for DiBP, 0.010 and 0.004 for DnBP, 0.021 and 0.025 for DEHP, respectively. Air-PM partition of DiBP and DnBP approached equilibrium, while that of DEHP did not reach equilibrium in either season. The impacts of built environmental conditions on phthalate concentrations were characterized. Elevated temperature resulted in accumulation of airborne phthalates. Higher air humidity led to more water absorption of aerosols in summer, facilitated mass transfer of phthalates from air to PM, and resulted in greater K of DiBP and DnBP in the summer. Any factors such as proximity to local traffic highway and indoor smoking activities, which can increase indoor PM concentrations, resulted in significantly higher airborne phthalate concentrations. Improving ventilation was not an effective measure to reduce indoor airborne phthalate concentrations.
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