Oliktok Point Site Science: Aerosols and their impacts on clouds

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Description

Evaluating aerosol properties has implications for the formation of Arctic clouds, resulting in impacts on cloud lifetime, precipitation processes, and radiative forcing. There are many remaining uncertainties and large discrepancies regarding modeled and observed Arctic aerosol properties, illustrating the need for more detailed observations to improve simulations of Arctic aerosol and more generally, projections of the components of the aerosol-driven processes that impact Arctic climate. Here, we present a comprehensive, long-term record of aerosol observations from the DOE ARM North Slope of Alaska site at Barrow. These measurements include total mass and number concentrations, chemical composition, particle size distributions, extinction, and aerosol optical depth (AOD) measurements. Aerosol extinction and number concentration measurements extend back to 1976, while the remaining measurements were implemented since. Corroboration between the ground-based chemical, physical, and optical property measurements is evident during periods of overlapping observations, demonstrating the reliability of the measurements. During the Arctic Haze in the winter/spring, high concentrations of long-range transported submicron sea salt, mineral dust, industrial metals, pollution (non-sea salt sulfate, nitrate, ammonium), and biomass burning species are observed concurrent with higher concentrations of particles with sizes that span the submicron range, enhanced absorption and scattering coefficients, and largest Ångström exponents. The summer is characterized by high concentrations of small biogenic aerosols (< 100 nm) and low extinction coefficients. Fall is characterized by clean conditions, with supermicron sea salt representing the dominant aerosol type supporting the highest single scattering albedos. In addition to evaluating the aerosol properties themselves, linkages between aerosol source and cloud ice water content in single layer mixed phase clouds are investigated during the winter/spring haze season, when the large influence from transported aerosols have the greatest potential to influence cloud formation. Finally, to complement relationships observed between the various ground-based in-situ measurements, seasonal surface-based estimated AOD is evaluated. This evaluation reveals that the in-situ seasonal patterns do not align with the seasonal cycle of the column AOD, demonstrating a discontinuity between near-surface and free tropospheric aerosols.