Ambient Gas/Particle Partitioning. 2: The Influence of Particle Source and Temperature on Sorption to Dry Terrestrial Aerosols

Abstract

In a companion paper we reported that, for apolar and most polar compounds, the dominating sorption mechanism governing ambient gas/particle partitioning under dry conditions is absorption into a water-insoluble organic matter (WIOM) phase, whereas under moist conditions, polar and ionized compounds can partition additionally into a mixed-aqueous phase. In order to understand how sorption into the WIOM varies for particles from diverse terrestrial locations, we looked at over 500 equilibrium gas/particle partitioning constants, Kip, measured at a specific temperature and relative humidity (15 degrees C, 50% RH), covering aerosol samples from all seasons and various locations. The data indicate that for every sample the WIOM exhibits similar intermolecular interactions with gas-phase organic compounds. For a given compound, the Kip values usually vary within a factor 3 for different aerosol samples, though they could vary by up to an order of magnitude. This is most likely due to variations in the WIOM weight fraction. Fitted poly parameter linear free energy relationships (PP-LFERs) were validated by giving good predictions of Kip values for many SVOCs in the literature, including n-alkanes, organochlorines, PCBs, though not PAHs as much of the particle-bound PAHs are likely nonexchangeable with the air phase. This study also investigated the influence of temperature on partitioning to WIOM, and found thatthe temperature dependence of Kip values can be reasonably predicted using the pure compound's enthalpy of vaporization.