Partitioning of 1,2-dichlorobenzene onto organic and inorganic aerosols

Abstract

Environmental context Contaminants adsorbed in aerosols are transported and deposited effectively to the respiratory system compared to their vapours. Measuring the extremely low concentration of highly volatile contaminants contained in aerosols is challenging; hence assessing their adverse effects on environmental and human health is less understood. The measured concentrations of these contaminants are similar to less volatile chemicals sampled from diverse environmental aerosols, suggesting that their contribution cannot be neglected. Abstract Volatile organic compounds (VOCs) are not expected to partition onto aerosols because of their high vapour pressure. Studies on gas–aerosol partitioning of VOCs have been limited because of the challenge in discriminating the small mass fraction of the VOCs in the aerosol relative to that in the gas phase. Here, we developed a bench-scale system to investigate the partitioning of a surrogate VOC, 1,2-dichlorobenzene (1,2-DCB), into inorganic and organic aerosols under different relative humidities (RHs) and temperatures. The partitioning coefficient (Kip) of 1,2-DCB into succinic acid (SA) aerosol was ~10× higher than those into ammonium sulfate (Am Sulf) aerosol. These Kip corresponded to 0.23–3.27 pg 1,2-DCB µg−1 of SA aerosol and 0.02–3.82 pg 1,2-DCB µg−1 of Am Sulf aerosol for RH levels of 5–95 %. Sorption of 1,2-DCB onto Am Sulf aerosol followed the classic relationship between Kip and RH, whereas that onto SA did not. For Am Sulf aerosols, RH levels exceeding 50 % have a negligible effect on partitioning, in which the extremely low amount of 1,2-DCB partitioned into the aerosol via dissolution. The octanol–air partition (KOA) model predicted the Kip of 1,2-DCB for SA aerosol better than the saturated vapour pressure partition (Pi0) model, whereas the Pi0 model predicted Kip better than the KOA model only when absorptive partitioning was considered.