10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Sensitivity of Sulfate In-cloud Chemistry and CCN Activation to pH Variability and Mixing State Using a Particle Resolved Model
YU YAO, Nicole Riemer, Matt Dawson, University of Illinois at Urbana-Champaign
Abstract Number: 790 Working Group: Aerosol Modeling
Abstract Over 50 percent of the total sulfate mass at the global scale is produced by in-cloud aqueous phase chemistry that oxidize S(IV) to S(VI), and the reactions can change the particle size distribution after cloud evaporation. It is well known that different reaction pathways contribute to these oxidation processes, and that the relative importance of the pathways depends on pH. However, for current regional and global scale models it is challenging to capture the effects of non-linearity in reaction rates that may occur due to differences in droplet composition in the highly externally mixed aerosol systems often found in the real atmosphere.
In this study, we focus on the sensitivity of sulfate formation to aerosol mixing state and related variations in pH across the particle population. We simulated several urban plume scenarios that produced populations with a wide range of different aerosol mixing states using the particle-resolved model PartMC-MOSAIC. These simulated aerosol populations were then used as the input for cloud parcel simulations including aqueous chemistry where we found the sulfuric species transition mainly between sulfate, bisulfite and hydrogen sulfate under different pH and oxidation environments. The aqueous chemistry mechanism coupled in the model is based on a reduced version of CAPRAM 2.4 developed by Ervens et al. in 2003, which includes 121 aerosol species and 178 reactions. The particle-resolved approach is well-suited for this problem because it can track the evolution of compositions in each particle, including the concentration of H+. We quantified how sulfate formation changes the CCN properties of the aerosol population after cloud evaporation and how this depends on the mixing state of the cloud-forming aerosol. The results will also be used to quantify the uncertainties of CCN properties due to the assumptions of the aerosol mixing state.