An improved representation of aerosol mixing state for air quality–weather interactions

Abstract. We implement a detailed representation of aerosol mixing state in the Global Environmental Multiscale – Modelling Air quality and CHemistry (GEM-MACH) air weather forecast model. Our mixing-state includes three categories: one for more hygroscopic aerosol, less with high black carbon (BC) mass fraction, low BC fraction. The allows us to better resolve two different aspects state: differences hygroscopicity due composition amount absorption enhancement non-absorbing coatings. Notably, this three-category account thickly coated primary organic matter, which enhances but has hygroscopicity. compare results (1L2B, (one hydrophilic, hydrophobic)) simulation that uses categories, split by (HYGRO), using original size-resolved internally mixed assumption (SRIM). perform case study is focused on North America during July 2016, when there were intense wildfires over northwestern America. find both 1L2B HYGRO decreases wet deposition, increases concentrations, particularly species. concentration PM2.5 23 % average. show these increased concentrations increase cloud droplet number reflectivity model, decreasing surface temperatures. Using categories based yields only modest benefit resolving coating thickness carbon, however. resolves thinner coatings than simulation, resulting optical depths are 3 average, greater strong anthropogenic source regions. did not subsequent effects decreased meteorology.