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

Abstract

Abstract. The sources, chemical transformations and removal mechanisms of aerosol\ntransported to the Arctic are key factors that control Arctic\naerosol–climate interactions. Our understanding of sources and processes is\nlimited by a lack of vertically resolved observations in remote Arctic\nregions. We present vertically resolved observations of trace gases and\naerosol composition in High Arctic springtime, made largely north of\n80 ∘ \u2009N, during the NETCARE campaign. Trace gas gradients observed on\nthese flights defined the polar dome as north of 66–68 ∘ \u200930 ′ \u2009N\nand below potential temperatures of 283.5–287.5\u2009K. In the polar dome, we\nobserve evidence for vertically varying source regions and chemical\nprocessing. These vertical changes in sources and chemistry lead to\nsystematic variation in aerosol composition as a function of potential\ntemperature. We show evidence for sources of aerosol with higher organic\naerosol (OA), ammonium and refractory black carbon (rBC) content in the upper\npolar dome. Based on FLEXPART-ECMWF calculations, air masses sampled at all\nlevels inside the polar dome (i.e., potential temperature K , altitude ∼ 3.5 km ) subsided during transport\nover transport times of at least 10\xa0days. Air masses at the lowest potential\ntemperatures, in the lower polar dome, had spent long periods ( >10 \xa0days)\nin the Arctic, while air masses in the upper polar dome had entered the\nArctic more recently. Variations in aerosol composition were closely related\nto transport history. In the lower polar dome, the measured sub-micron\naerosol mass was dominated by sulfate (mean 74\u2009%), with lower contributions from rBC (1\u2009%), ammonium (4\u2009%) and OA\n(20\u2009%). At higher altitudes and higher potential temperatures, OA,\nammonium and rBC contributed 42\u2009%, 8\u2009% and 2\u2009% of aerosol mass,\nrespectively. A qualitative indication for the presence of sea salt showed\nthat sodium chloride contributed to sub-micron aerosol in the lower polar\ndome, but was not detectable in the upper polar dome. Our observations\nhighlight the differences in Arctic aerosol chemistry observed at\nsurface-based sites and the aerosol transported throughout the depth of the\nArctic troposphere in spring.