Measurement of the Diffusion and Partition Coefficients of 6-Methyl-5-hepten-2-one in Clothing

Deep understanding of the chemical reaction and physical transport characteristics of 6-methyl-5-hepten-2-one (6-MHO) in different phases (e.g., skin, clothing) is important for modeling the indoor squalene/ozone reaction. In this study, we make the first attempt to accurately measure the physical transport parameters, i.e., the diffusion coefficient (D_m) and partition coefficient (K) of 6-MHO in different clothing (jeans, nylon, pure cotton T-shirt). A ventilated-airtight-ventilated testing procedure was designed, and relevant experiments were performed in 30 L small-scale chambers. The key parameters of 6-MHO (D_m and K) are determined by nonlinearly fitting the measured gas-phase concentration data with physical model using a hybrid optimization method. The high fitting accuracy (R² > 0.93), good replication (relative deviations of determined D_m and K less than 16% for duplicated experiments), and further sensitivity analysis demonstrate the reliability and robustness of the method. In addition, the variation of the key parameters of 6-MHO in the pure cotton T-shirt with temperature (in the range of 20-37 °C) is investigated. Results indicate that D_m increases while K decreases with increasing temperature. This study provides some of the fundamental data for characterizing the squalene/ozone reaction and should be helpful for the subsequent dermal exposure in realistic indoor environments.