From a polar to a marine environment: has the changing Arctic led to a shift in aerosol light scattering properties?

• Main Authors: Heslin-Rees, Dominic, Burgos, Maria, Hansson, Hans-Christen, Krejci, Radovan, Ström, Johan, Tunved, Peter, Zieger, Paul
• Format: Text
• Language: English
• Published: 2020
• Subjects: Arctic; Svalbard; Climate change; Sea ice
• Online Access: https://doi.org/10.5194/acp-2020-521; https://www.atmos-chem-phys-discuss.net/acp-2020-521/

The study of long-term trends in aerosol optical properties is an important task to understand the underlying aerosol processes influencing the change of climate. The Arctic, as the place where climate change manifests most, is an especially sensitive region of the world. Within this work, we use a unique long-term data record of key aerosol optical properties from Zeppelin observatory, Svalbard, to ask the question of whether the environmental changes of the last two decades in the Arctic are reflected in the observations. We perform a trend analysis of the measured particle light scattering and backscattering coefficients and the derived scattering Ångström exponent and hemispheric backscattering fraction. In contrast to previous studies, the effect of in-cloud scavenging and potential sampling losses at the site is taken explicitly into account in the trend analysis. The analysis is combined with a back trajectory analysis and satellite-derived sea ice data, to support the interpretation of the observed trends. We find that the optical properties of aerosol particles have undergone clear and significant changes in the past two decades. The scattering Angström exponent and the particle light scattering coefficient exhibit statistically significant decreasing of between −4.9 and −6.3 % per year (using wavelengths of λ = 450 and 550 nm) and increasing trends of between 2.3 and 2.9 % per year (at a wavelength of λ = 550 nm), respectively. The magnitudes of the trends vary depending on the season. These trends indicate a shift to an aerosol dominated more by coarse-mode particles, most likely the result of increases in the relative amount of sea spray aerosol. We show that changes in air mass circulation patterns, specifically an increase in air masses from the south-west, are responsible for the shift in aerosol optical properties, while the decrease of Arctic sea ice in the last two decades had only a marginal influence on the observed trends.