The gas/particle partitioning behavior of phthalate esters in indoor environment: Effects of temperature and humidity.

Phthalate esters (PAEs) are ubiquitous and among the most abundant semi-volatile organic compounds (SVOCs) in indoor environments. Due to their low saturated vapor pressure, SVOCs tend to adhere to indoor surfaces and particulate matters, which may result in higher total concentrations than occur in the gas phase alone. Thus, gas/particle partitioning of PAEs plays an important role in their indoor fates and health risks. However, the influence of indoor environmental parameters, including temperature and humidity, on the partitioning of PAEs between air and particles is rarely known. In this study, a novel experimental system was designed to investigate the effects of temperature and humidity on partitioning behavior between gas- and particle-phase PAEs. The chamber experiments were conducted at temperatures of 12.5 °C, 17.5 °C, 24.0 °C, 29.5 °C and 40.0 °C and moisture contents of 3.5 g/kg, 5.0 g/kg, 6.5 g/kg, 8.0 g/kg and 9.5 g/kg dry air. The results showed that higher temperatures led to stronger emission of phthalate esters from the PVC panel, which resulted in higher gas-phase concentrations of phthalate esters and particle-phase concentrations. In addition, temperature has a strong negative effect on the gas/particle partition coefficient (Kp), and an order of magnitude difference in Kp was observed between 12.5 and 40 °C. There are exponential decay laws between Kp and the absolute temperature. However, a smaller effect of humidity than of temperature on Kp was revealed, and no obvious law was found. Moreover, Kp of compounds with larger molecular weights are more obviously influenced by the variations in environmental factors. This study is of positive significance for reducing the health risks of PAEs by guiding the regulation of indoor environmental parameters.