AS&T virtual collection: Aerosol particle physical chemistry

AS&T virtual collection: Aerosol particle physical chemistryThe physicochemical properties of aerosol particles, including particle pH, phase, viscosity, surface tension, and hygroscopicity, are critical to our understanding of aerosol dynamics and transformations.These particle properties influence key complex processes such as particle growth and phase transitions, heterogeneous and multiphase chemistry, gas-surface-bulk partitioning, aerosol optical properties, cloud droplet activation, and ice nucleation.Over the past years it has become evident that some barriers to our understanding of aerosol physical chemistry can only be addressed through new fundamental laboratory, theoretical, and modeling studies.Aerosol physical chemistry is an important area of focus and interest in the aerosol community.In May 2022, we organized the 5th biennial conference entitled "A Molecular-Level Understanding of Atmospheric Aerosols" (MUOAA 2022), bringing together an international community of researchers interested in all aspects of the molecular chemistry and physics of aerosols.The conference provided a unique forum for the participants to exchange ideas on treating aerosol physical chemistry.Support from the National Science Foundation also made it particularly possible for early career aerosol scientists to attend.In MUOAA 2022, discussion points that crossed over many categories included aerosol pH, defining and understanding surfaces, limits of detections and biases for varied measurement techniques, appropriate model/surrogate chemical systems, and how to incorporate measurements into models.Similarly, in October 2022, the AAAR Special Symposium "Aerosol Physical Chemistry and Microphysics", organized by Cari Dutcher as well as Sarah Petters (Aarhus University) and Miriam Freedman (Pennsylvania State University), sought to stimulate interdisciplinary discussion in fundamental aerosol physical chemistry and microphysical phenomena, bridging scales and using computational, experimental, and observational techniques.This AS&T special issue was born out of these workshops, seeking to collect a series of papers from participants from MUOAA 2022 and beyond.In particular, motivated by the discussions at the 2022 workshops, we sought topics on (1) Particle surfaces: Defining and understanding surface properties coupled with advanced and emerging measurement and modeling methods, surfactants and surface rheology, bulk-surface-gas partitioning, reactions, and mass transfer, on (2) Particle phase: Particle hygroscopicity,