Exploring the Influence of Environmental Conditions on the Gas-Particle Partitioning of Organic Acids and Bases in the Greater Toronto Area
OLIVIA DRIESSEN, Ye Tao, Xiaoying Yang, Matthew Davis, Yutong Wang, Laura-Helena Rivellini, Jonathan Abbatt, Jennifer Murphy, Mayré Rodriguez Ramirez, RenXi Ye, Cora Young, Trevor VandenBoer, Sumi Wren, Jeremy Wentzell, Michael Wheeler, Alex K.Y. Lee, Elisabeth Galarneau, University of Toronto
Abstract Number: 457
Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene
Abstract
The gas-particle partitioning of low-volatility and semi-volatile organic compounds (L/S-VOCs) plays a dominant role in the formation and growth of secondary organic aerosol. Improved knowledge of these processes is needed to better understand the health and climate effects of atmospheric particulate matter (PM), as well as the fates of various airborne pollutants. The phase distribution of L/SVOCs in the atmosphere can be impacted by environmental conditions such as temperature, the existing concentration of organic PM, and aerosol liquid water content (LWC). For many ionizable compounds, aerosol pH can also have a strong influence on partitioning. As SO2 and NOx emissions decrease and NHx species increasingly dominate the buffer capacity of the atmospheric aqueous phase, wide variations in aerosol pH have been observed, carrying implications for the role of ionizable organics in aqueous PM. This project aims to investigate the impact of changing atmospheric conditions on the gas-particle partitioning of ionizable organic compounds, using summertime and wintertime measurements from two field campaigns conducted in the Greater Toronto Area (THECIX, July-August 2023; SWAPIT, January-March 2024). Applying a chemical partitioning space analysis that considers the impacts of pH, we estimate the phase distribution of a collection of semi-volatile organic acids and bases (e.g., trifluoroacetic acid, pyruvic acid, levulinic acid, pinonic acid, hydroxybutyric acid, monochloroacetic acid, oxalic acid, succinic acid, glutaric acid, malonic acid, pinic acid, phthalic acid, adipic acid, and several short-chain alkylamines) during the measurement periods. We assess the effects of temperature, relative humidity, aerosol LWC, pH, and organic aerosol loading on the partitioning behavior of these compounds. Gas- and particle-phase measurements on AIM-IC and SP-AMS are used to inform our modeling efforts, and predicted gas-particle partitioning is compared to measurements of organics on iodide-CIMS, MOUDI, and AIM-IC-MS.