Chemical composition and source attribution of sub-micrometre aerosol particles in the summertime Arctic lower troposphere

Andreas.Herber [ at ]


Aerosol particles impact the Arctic climate system both directly and indirectly by modifying cloud properties, yet our understanding of their vertical distribution, chemical composition, mixing state, and sources in the summertime Arctic is incomplete. In situ vertical observations of particle properties in the high Arctic combined with modelling analy- sis on source attribution are in short supply, particularly dur- ing summer. We thus use airborne measurements of aerosol particle composition to demonstrate the strong contrast be- tween particle sources and composition within and above the summertime Arctic boundary layer. In situ measure- ments from two complementary aerosol mass spectrometers, the Aircraft-based Laser Ablation Aerosol Mass Spectrom- eter (ALABAMA) and an Aerodyne high-resolution time- of-flight aerosol mass spectrometer (HR-ToF-AMS), are pre- sented alongside black carbon measurements from an single particle soot photometer (SP2). Particle composition anal- ysis was complemented by trace gas measurements, satel- lite data, and air mass history modelling to attribute parti- cle properties to particle origin and air mass source regions. Particle composition above the summertime Arctic bound- ary layer was dominated by chemically aged particles, con- taining elemental carbon, nitrate, ammonium, sulfate, and organic matter. From our analysis, we conclude that the pres- ence of these particles was driven by transport of aerosol and precursor gases from mid-latitudes to Arctic regions. Specifically, elevated concentrations of nitrate, ammonium, and organic matter coincided with time spent over vegeta- tion fires in northern Canada. In parallel, those particles were largely present in high CO environments (> 90 ppbv ). Ad- ditionally, we observed that the organic-to-sulfate ratio was enhanced with increasing influence from these fires. Besides vegetation fires, particle sources in mid-latitudes further in- clude anthropogenic emissions in Europe, North America, and East Asia. The presence of particles in the Arctic lower free troposphere, particularly sulfate, correlated with time spent over populated and industrial areas in these regions. Further, the size distribution of free tropospheric particles containing elemental carbon and nitrate was shifted to larger diameters compared to particles present within the boundary layer. Moreover, our analysis suggests that organic matter, when present in the Arctic free troposphere, can partly be identified as low molecular weight dicarboxylic acids (ox- alic, malonic, and succinic acid). Particles containing dicar- boxylic acids were largely present when the residence time of air masses outside Arctic regions was high. In contrast particle composition within the marine boundary layer was largely driven by Arctic regional processes. Air mass history modelling demonstrated that alongside primary sea spray particles, marine biogenic sources contributed to secondary aerosol formation via trimethylamine, methanesulfonic acid, sulfate, and other organic species. Our findings improve our knowledge of mid-latitude and Arctic regional sources that influence the vertical distribution of particle chemical com- position and mixing state in the Arctic summer.

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Köllner, F. , Schneider, J. , Willis, M. D. , Schulz, H. , Kunkel, D. , Bozem, H. , Hoor, P. M. , Klimach, T. , Helleis, F. , Burkart, J. , Leaitch, W. R. , Aliabadi, A. A. , Abbatt, J. P. , Herber, A. and Bohrmann, S. (2021): Chemical composition and source attribution of sub-micrometre aerosol particles in the summertime Arctic lower troposphere , Atmospheric Chemistry and Physics, 21 , pp. 6509-6539 .

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POLAR 5 > P5_205_PAMARCMIP_2017

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