Aerosol Acidity Controls Methanesulfonic Acid Evaporation From Aerosols During Antarctic Katabatic Outflow

Methanesulfonic acid (MSA), a key oxidation product of dimethyl sulfide (DMS), plays a crucial role in the atmospheric sulfur cycle and in the formation of cloud condensation nuclei (CCN). MSA contributes significantly to aerosol growth and, potentially, the modulation of cloud microphysical properties, particularly in remote marine and polar regions where CCN concentrations are relatively low. Here we focus on an eight-day period of elevated gaseous MSA observed along the coastal region of East Antarctica that coincided with persistent katabatic outflow. We show that this outflow brings biogenically dominated, highly acidic aerosols with elevated gaseous MSA resulting from evaporation off the surface of these aerosol particles. While MSA evaporation is promoted by a decrease in relative humidity, we show that aerosol acidity is the primary driver of this process. These results provide new insights into processes involved in the marine sulfur cycle, which should be included when using observations of DMS oxidation products to guide model evaluation and development. Furthermore, they reveal the highly acidic nature of Southern Ocean aerosols and highlight the importance of aerosol acidity on atmospheric processes.