Lawler, M. J.Saltzman, E. S.Karlsson, L.Zieger, P.Salter, M.Baccarini, A.Schmale, J.Leck, C.2021-11-072021-11-072021-11-072021-11-0610.1029/2021GL094395https://infoscience.epfl.ch/handle/20.500.14299/182936The summertime high Arctic atmosphere is characterized by extremely low aerosol abundance, such that small natural aerosol inputs have a strong influence on cloud formation and surface temperature. The physical sources and the mechanisms responsible for aerosol formation and development in this climate-critical and changing region are still uncertain. We report time-resolved measurements of high Arctic Aitken mode (∼20–60 nm diameter) aerosol composition during August–September 2018. During a significant Aitken mode formation event, the particles were composed of a combination of primary and secondary materials. These results highlight the importance of primary aerosol sources for high Arctic cloud formation, and they imply the action of a poorly understood atmospheric mechanism separating larger particles into multiple sub-particles.text::journal::journal article::research article