Size-resolved atmospheric particulate polysaccharides in the high summer Arctic

Abstract

Abstract. Size-resolved aerosol samples for subsequent quantitative determination of polymer sugars (polysaccharides) after hydrolysis to their subunit monomers (monosaccharides) were collected in surface air over the central Arctic Ocean during the biologically most active summer period. The analysis was carried out by novel use of liquid chromatography coupled with highly selective and sensitive tandem mass spectrometry. Polysaccharides were detected in particle sizes ranging from 0.035 to 10 µm in diameter with distinct features of heteropolysaccharides, enriched in xylose, glucose + mannose as well as a substantial fraction of deoxysugars. Polysaccharides, containing deoxysugar monomers, showed a bimodal size structure with about 70 % of their mass found in the Aitken mode over the pack ice area. Pentose (xylose) and hexose (glucose + mannose) had a weaker bimodal character and were largely found with super-micrometer sizes and in addition with a minor submicrometer fraction. The concentration of total hydrolysable neutral sugars (THNS) in the samples collected varied over two orders of magnitude (1 to 160 pmol m −3 ) in the supermicrometer size fraction and to a somewhat lesser extent in sub-micrometer particles (4 to 140 pmol m −3 ). Lowest THNS concentrations were observed in air masses that had spent more than five days over the pack ice. Within the pack ice area, about 53 % of the mass of hydrolyzed polysaccharides was detected in sub-micrometer particles. The relative abundance of sub-micrometer hydrolyzed polysaccharides could be related to the length of time that the air mass spent over pack ice, with the highest fraction (> 90 %) observed for > 7 days of advection. The aerosol samples collected onboard ship showed similar monosaccharide composition, compared to particles generated experimentally in situ at the expedition's open lead site. This supports the existence of a primary particle source of polysaccharide containing polymer gels from open leads by bubble bursting at the air-sea interface. We speculate that the occurrence of atmospheric surface-active polymer gels with their hydrophilic and hydrophobic segments, promoting cloud droplet activation, could play a potential role as cloud condensation nuclei in the pristine high Arctic.

Potential source regions and processes of aerosol in the summer Arctic

“…For the former case, this may involve both direct emissions of larger polymer gel accumulation-mode particles and the growth of smaller particles via two processes, namely heterogeneous condensation and aerosol cloud processing in which the bimodal particle size distribution characteristic of cloud-processed air is created (Hoppel et al, 1994). Previous studies in the same area and season (Heintzenberg et al, 2006;Chang et al, 2011;Heintzenberg and Leck, 2012;Kupiszewski et al, 2013;Hellén et al, 2012;Nilsson and Leck, 2002;Leck et al, 2013;Leck and Persson, 1996b;Leck and Bigg, 2005) have shown raised concentrations of accumulation-mode particles within the high Arctic boundary layer which the authors attribute to sources upwind Oden: transport of precursor gases and marine biogenic particles from the MIZ or locally from open leads over the pack ice. Previously reported results of individual particles by Leck (2001, 2008), Leck et al (2002), and Bigg (2005a, b, 2010) collected over the pack ice however have failed to find evidence of sea salt particles of less than 200 nm in diameter.…”

“…The colors correspond to those in Fig. 13. ings includes the fact that near-surface airborne aerosol, as well as low-level cloud and fog droplets, contained the same type of polymer gel material as found in the open-lead surface microlayer (Gao et al, 2012;Leck et al, 2013;Orellana et al, 2011;Bigg et al, 2004;Leck and Bigg, 2005).…”

“…Schematic view of the sources and transport mechanisms of aerosol particles over the summer Arctic pack ice, adapted from Kupiszewski et al (2013). zone (MIZ) or locally from open leads 2 over the pack ice has been found to result in raised concentrations of accumulation-mode particles within the high Arctic boundary layer (Heintzenberg et al, 2006;Chang et al, 2011;Heintzenberg and Leck, 2012;Kupiszewski et al, 2013;Hellén et al, 2012;Nilsson and Leck, 2002;Leck et al, 2013). This may involve both direct emissions of primary larger accumulation-mode marine particles, as well as growth of smaller particles via two processes, namely heterogeneous condensation and aerosol cloud processing.…”

“…The polymer gels are made up of water-insoluble, heat-resistant, highly surface-active and highly hydrated (99 % water) polysaccharide molecules spontaneously forming three-dimensional networks inter-bridged with divalent ions (Ca 2+ /Mg 2+ ), to which other organic compounds, such as proteins and lipids, are readily bound (Gao et al, 2011;Leck et al, 2013;Orellana et al, 2011;. 2 The high Arctic open leads can be described as ever-changing open water channels comprising 10-30 % of the ice pack ice area, ranging from a few meters up to a few kilometers in width.…”

Aerosol and snow transfer processes: An investigation on the behavior of water-soluble organic compounds and ionic species

“…S5). The additional occurrence of glucose in the coarse particles (>1 mm) may be due to degradation of polysaccharides occurred during long range transport processes (Leck et al, 2013). Biological degradation, as a source of sugars, is also indicated by the higher mean concentration of sucrose (96 pg m À3 ) in the 2014e2015 samples compared to the mean concentration (3 pg m À3 ) in the 2010e2011 samples (Barbaro et al, 2015a).…”