Processes Controlling the Composition and Abundance of Arctic Aerosol

The Arctic region is a harbinger of global change and is warming at a rate higher than the global average. While Arctic warming is driven by increases in anthropogenic greenhouse gases' in combination with local feedback mechanisms, short-lived climate forcing agents, such as tropospheric aerosol, are also important drivers of Arctic climate. Arctic aerosol-climate impacts vary seasonally as a result of the interplay between aerosol and different cloud types, available solar radiation, sea ice, surface albedo, Arctic and lower latitude removal processes, and atmospheric transport patterns. Photochemistry and efficient wet aerosol removal have low impact in winter but become important in spring to summer, dramatically altering aerosol chemical composition, and driving the size distribution from a pronounced accumulation mode toward a dominance of smaller particles. Retreating sea ice, increasing solar insolation and warmer temperatures in summer result in enhanced emissions from Arctic marine and terrestrial ecosystems, and anthropogenic sources, with impacts on the composition of gas and particle phases. Fractional cloud cover reaches a maximum in Arctic summer, in parallel with decreasing sea ice extent and surface albedo. This seasonal variation corresponds to significant changes in the net cloud radiative effect; changes that are affected by aerosol. This review summarizes our current knowledge of processes that control Arctic aerosol properties. We highlight both natural and anthropogenic processes that will be impacted by current and future sea ice loss. Efforts are needed to better constrain aerosol removal rates, characterize aerosol precursors, and constrain the seasonality and magnitude of aerosol-cloud-climate impacts. Plain Language Summary The Arctic environment is changing rapidly. While Arctic climate change is mostly driven by increases in greenhouse gases produced by human activity, other human-induced and natural emissions also influence climate. We focus on the role of atmospheric aerosol in Arctic regions. In this article, we summarize the current state of knowledge of the various processes that drive the climate-relevant properties of aerosol in the Arctic. We emphasize the processes that arise from interactions between the atmosphere, ocean, land, and ice-covered areas and the impact of aerosol on clouds at high latitudes. These processes are all being impacted by Arctic warming and sea ice loss. We need to understand these processes in order to understand past and future changes in Arctic climate.