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

Andreas.Herber [ at ]


The sources, chemical transformations and re- moval 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 re- gions. We present vertically resolved observations of trace gases and aerosol composition in High Arctic springtime, made largely north of 80◦ N, during the NETCARE cam- paign. Trace gas gradients observed on these flights defined the polar dome as north of 66–68◦ 30′ N and below poten- tial temperatures of 283.5–287.5 K. 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), ammo- nium 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., po- tential temperature < 280.5 K, altitude <∼ 3.5 km) subsided during transport over transport times of at least 10 days. Air masses at the lowest potential temperatures, in the lower po- lar dome, had spent long periods (> 10 days) in the Arc- tic, while air masses in the upper polar dome had entered the Arctic more recently. Variations in aerosol composition were closely related to transport history. In the lower polar dome, the measured sub-micron aerosol mass was dominated by sulfate (mean 74 %), with lower contributions from rBC (1 %), ammonium (4 %) and OA (20 %). At higher altitudes and higher potential temperatures, OA, ammonium 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 po- lar dome. Our observations highlight the differences in Arc- tic aerosol chemistry observed at surface-based sites and the aerosol transported throughout the depth of the Arctic tropo- sphere in spring.

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DOI 10.5194/acp-19-57-2019

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Willis, M. D. , Bozem, H. , Kunkel, D. , Lee, A. K. , Schulz, H. , Burkart, J. , Aliabadi, A. A. , Herber, A. , Leaitch, W. R. and Abbatt, J. P. (2019): Aircraft-based measurements of High Arctic springtime aerosol show evidence for vertically varying sources, transport and composition , Atmos. Chem. Phys., 19 , pp. 57-76 . doi: 10.5194/acp-19-57-2019

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