Ice nucleation ability of different desert dusts during PIANO chamber campaigns

Ice nucleating particles (INPs) are a minor subset of atmospheric aerosols that can influence clouds, precipitation and climate by promoting the formation of ice at warm temperatures. Mineral dust is a dominant source of INPs in the atmosphere because of its relatively high ice nucleating efficiency and abundance. Despite its importance, there are considerable uncertainties about the impacts of atmospheric processing (chemical "aging") on the INP activity of dust - especially on the role of species that acidify (like sulfuric acid and nitric acid) upon condensation onto INPs.Motivated by the above uncertainties, we carry out the CleanCloud PIANO campaigns - which involve laboratory studies of the INP activity of dust generated from soils originating from Iceland, Morocco, and Chile. We study the properties of freshly generated dust, as well as dust that has been exposed to acidic species (HNO3 and H2SO4) using the FORTH/ICEHT environmental chamber facility in Patras, Greece. Dust was generated two ways - using a cyclone generator in the case of fresh dust, or mixed with sea salt using the AEGOR sea spray simulation chamber.INP activity was measured online with a Portable Ice Nucleation Experiment (PINE) and offline using a cold-plate droplet freezing assay on dust samples collected from the chamber using an impinger. Size-resolved INP was also characterized using an Aerodynamic Aerosol Classifier (AAC) to select dust particles below a defined size cut prior to entering the PINE instrument.Our results show that aging by acidification can strongly suppress the ice nucleation efficiency of mineral dust. In particular, aging reduced mass-normalized INP concentrations by a median of 86.3% for Icelandic dust, 77.2% for Moroccan dust, and 84.7% for Chilean dust across the investigated temperature range, demonstrating that chemical processing during atmospheric transport can substantially weaken the ability of desert dust particles to act as INPs.