Super micron Amazonian aerosol particles as efficient catalyzers at cirrus temperatures

Ice-containing clouds are key players in the climate system; however, they remain highly uncertain, especially in tropical latitudes. Cirrus clouds are common over Amazonia; nevertheless, there have been no quantitative deposition ice nucleation measurements in this rainforest. Here we present the ice nucleating abilities of aerosol particles in northwestern Amazonia at thermodynamic conditions relevant to mixed-phase and cirrus clouds during the biomass burning and rainy seasons. We show that background particles control mixed-phase cloud formation, with comparable ice nucleating particle concentrations in central and northwestern Amazonia. We also observed that super-micron Amazonian particles are highly efficient at catalyzing cirrus clouds, with higher efficiency at lower temperatures. These super-micron particles are likely from local sources and single particle analysis indicates that they are enriched in organics and mineral dust. Our results highlight the importance of Amazonian super-micron particles active at temperatures found in cirrus clouds, if found in sufficient concentrations in the upper troposphere, with implications for the planetary radiative balance.