Arctic Aerosol Surface-Column Partitioning and Radiative Forcing Potential

Due to rapid warming, the Arctic is moving toward a new state characterized by less sea ice and increasingly earlier snowmelt. Coupled with these changes in surface conditions, radiative forcing of aerosols, clouds, and variability in precipitation control vertical and horizontal heat exchange and atmospheric circulation patterns that further drive changes in air temperature. The role of aerosol in this complex and intricately coupled system is not well-known. Aerosols can impact radiative forcing and precipitation year-round in the Arctic through their modification of cloud properties, surface reflectivity, and attenuation of radiation in the otherwise clear atmosphere. The sources, properties, and distributions of aerosols that govern these impacts are in turn strongly dependent on surface cover and atmospheric circulation patterns. Most of our knowledge of Arctic aerosols comes from in situ measurements at the surface because they can be made continuously throughout the polar summer and winter. However, an examination of the differences in seasonal and inter-annual patterns of surface in situ and column aerosol extinction reveal significant differences that may alter our understanding of aerosol forcing, especially in their interactions with low clouds. Here we examine the persistent, seasonal differences in surface and column aerosol properties, inter-annual variability in these differences, likely drivers such as biomass burning events and changes in other dominant sources, and the radiative forcing implications as the surface and atmospheric state continues to change in the Arctic. Finally, we make an argument for the necessity of alternative aerosol observations such as lunar photometry and in situ measurements on unmanned aerial systems that fill the gaps in observations of column aerosol properties throughout the polar annual cycle.