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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-628
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Aug 2018

Research article | 24 Aug 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Aircraft measurements of High Arctic springtime aerosol show evidence for vertically varying sources, transport and composition

Megan D. Willis1, Heiko Bozem2, Daniel Kunkel2, Alex K. Y. Lee3, Hannes Schulz4, Julia Burkart5, Amir A. Aliabadi6, Andreas B. Herber4, W. Richard Leaitch7, and Jonathan P. D. Abbatt1 Megan D. Willis et al.
  • 1University of Toronto, Department of Chemistry, Toronto, Ontario, Canada
  • 2Johannes Gutenberg University of Mainz, Institute for Atmospheric Physics, Mainz, Germany
  • 3National University of Singapore, Department of Civil and Environmental Engineering, Singapore
  • 4Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany
  • 5University of Vienna, Faculty of Physics, Aerosol Physics and Environmental Physics, Vienna, Austria
  • 6School of Engineering, University of Guelph, Guelph, Ontario, Canada
  • 7Environment and Climate Change Canada, Toronto, Ontario, Canada

Abstract. The sources, chemical transformations and removal mechanisms of aerosol transported to the Arctic are key factors that control Arctic aerosol-climate interactions. Our understanding of sources and processes is limited by a lack of vertically resolved observations in remote Arctic regions. We present vertically resolved observations of trace gases and aerosol composition in High Arctic springtime, made largely north of 80°N, during the NETCARE campaign. Trace gas gradients observed on these flights defined the polar dome as north of 66–68.5°N and below potential temperatures of 283.5–287.5K (Bozem et al., 2018). In the polar dome, we observe evidence for vertically varying source regions and chemical processing. These vertical changes in sources and chemistry lead to systematic variation in aerosol composition as a function of potential temperature. We show evidence for sources of aerosol with higher organic aerosol (OA), ammonium (NH4) and refractory black carbon (rBC) content in the upper polar dome. Based on FLEXPART-ECMWF calculations, air masses sampled at all levels inside the polar dome (i.e., potential temperature <280.5K, altitude <∼3.5km) subsided during transport over transport times of at least 10days. Air masses at the lowest potential temperatures, in the lower polar dome, had spent long times (>10days) in the Arctic, while air masses in the upper polar dome had entered the Arctic more recently. These differences in transport history were closely related to aerosol composition. In the lower polar dome, the measured sub-micron aerosol mass was dominated by sulphate (mean 74%), with lesser contributions from rBC (1%), NH4 (4%) and OA (20%). At higher altitudes and warmer potential temperatures, OA, NH4 and rBC contributed 42%, 8% and 2% of aerosol mass, respectively. A qualitative indication for the presence of sea salt showed that sodium chloride contributed to sub-micron aerosol in the lower polar dome, but was not detectable in the upper polar dome. Our observations suggest that long-term, surface-based measurements underestimate the contribution of OA, rBC and NH4 to aerosol transported to the Arctic troposphere in spring.

Megan D. Willis et al.
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The vertical distribution of Arctic aerosol is an important driver of its climate impacts. We present vertically-resolved measurements of aerosol composition and properties made in the High Arctic during spring on an aircraft platform. We explore how aerosol properties are related to transport history and show evidence vertical trends in aerosol sources, transport mechanisms and composition. These results will help us to better understand aerosol-climate interactions in the Arctic.
The vertical distribution of Arctic aerosol is an important driver of its climate impacts. We...
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