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Abstract:
The Arctic climate is warming rapidly compared to other regions of the globe with drastic implications for its environment (e.g. sea ice loss). Aerosol particles are an important factor for the energy budget in this polar region as they interact directly or indirectly via cloud formation and processing with solar and terrestrial radiation. However, the interaction between aerosol and clouds in the Arctic is still not fully understood. This study focuses on the occurrence of different aerosol species and their influence on cloud processes in the summertime Arctic. Airborne in-situ measurements of particle composition were conducted in the European Arctic using the single particle mass spectrometer ALABAMA. Ambient aerosol particles and cloud particle residues in the diameter range between 250 nm and 1.6 µm were chemically analyzed. More than 240000 single particle mass spectra were obtained in total during the flights, almost 45000 of them from cloud residuals sampled in clouds. Different particle types were identified by detection of characteristic ion signal markers. This chemical particle analysis was complemented by further measurements of aerosol and cloud properties, trace gases as well as air mass history simulations. This study has found that Arctic cloud residual composition was dominated by triethyl- and/or diethylamine, which were observed for the first time in Arctic aerosol particles. In addition to amines, also sea spray, dicarboxylic acids, nitrate, iodine and elemental carbon were enriched inside the cloud residuals. In contrast, particles in ambient air contained mainly trimethylamine and sea spray inside the boundary layer and ammonium sulfate in the free troposphere. Only little contribution of triethyl- and/or diethylamine to particle composition in ambient air was observed, suggesting these amines were taken up by the cloud droplets from the gas-phase. This hypothesis was further supported by the observed correlation between the ethylated amine fraction and cloud liquid water content indicating their high solubility. Outside the Arctic, a significant contribution of these amines was found in clouds at mid-latitudes as well, suggesting a general importance of amines for cloud processes. Moreover, the cloud residual composition of clouds, which were thermodynamically decoupled from the surface, showed similarities to above-cloud particle composition. Thus, the thermodynamic structure of the clouds seems to play a critical role for the contribution of surface-related aerosol species to Arctic clouds.
