Abstract
Abstract. 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 analysis on source attribution are in short supply, particularly during summer. We thus use airborne measurements of aerosol particle composition to demonstrate the strong contrast between particle sources and composition within and above the summertime Arctic boundary layer. In situ measurements from two complementary aerosol mass spectrometers, the Aircraft-based Laser Ablation Aerosol Mass Spectrometer (ALABAMA) and an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), are presented alongside black carbon measurements from an single particle soot photometer (SP2). Particle composition analysis was complemented by trace gas measurements, satellite data, and air mass history modelling to attribute particle properties to particle origin and air mass source regions. Particle composition above the summertime Arctic boundary layer was dominated by chemically aged particles, containing elemental carbon, nitrate, ammonium, sulfate, and organic matter. From our analysis, we conclude that the presence 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 vegetation fires in northern Canada. In parallel, those particles were largely present in high CO environments (> 90 ppbv). Additionally, 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 include 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 (oxalic, malonic, and succinic acid). Particles containing dicarboxylic 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 composition and mixing state in the Arctic summer.
Highlights
In the face of rapid climate changes in the Arctic (IPCC, 2014, 2018), polar research has intensified to understand the key processes driving these changes and their effects on the Arctic environment (e.g., Serreze and Francis, 2006; Serreze et al, 2009; Flanner et al, 2011; Stroeve et al, 2012; Pithan and Mauritsen, 2014)
Overall, modelling studies focusing on aerosol–radiation interactions demonstrate that reductions in Arctic anthropogenic aerosol likely contributed to the observed Arctic surface warming in recent decades (e.g., Shindell and Faluvegi, 2009; Najafi et al, 2015; Acosta Navarro et al, 2016; Breider et al, 2017)
By means of the Aircraft-based Laser Ablation Aerosol Mass Spectrometer (ALABAMA), 10137 particles were analyzed during the NETCARE 2014 study when sampling outside clouds; 94 % of the spectra include size information, and 78 % of the spectra have dual polarity (Fig. 4)
Summary
In the face of rapid climate changes in the Arctic (IPCC, 2014, 2018), polar research has intensified to understand the key processes driving these changes and their effects on the Arctic environment (e.g., Serreze and Francis, 2006; Serreze et al, 2009; Flanner et al, 2011; Stroeve et al, 2012; Pithan and Mauritsen, 2014). Detailed knowledge of the vertical structure of aerosol composition and mixing state, as well as the related particle sources, formation, and ageing processes, are necessary to have a predictive understanding of our Arctic climate system; yet, the vertical distribution of summertime Arctic aerosol is not well represented in Arctic models (e.g., Quinn et al, 2008; Moore et al, 2011; Eckhardt et al, 2015; Sato et al, 2016; Sand et al, 2017; Willis et al, 2018; Abbatt et al, 2019; Schmale et al, 2021). This is the first comprehensive source attribution study of summertime Arctic aerosol composition, combining airborne single-particle and bulk chemical composition methods, with focus on the vertical structure
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