Size-resolved morphological properties of the high Arctic summer aerosol during ASCOS-2008

Abstract

Abstract. The representation of aerosol properties and processes in climate models is fraught with large uncertainties. Especially at high northern latitudes a strong underprediction of aerosol concentrations and nucleation events is observed and can only be constrained by in situ observations based on the analysis of individual aerosol particles. To further reduce the uncertainties surrounding aerosol properties and their potential role as cloud condensation nuclei this study provides observational data resolved over size on morphological and chemical properties of aerosol particles collected in the summer high Arctic, north of 80° N. Aerosol particles were imaged with scanning and transmission electron microscopy and further evaluated with digital image analysis. In total, 3909 aerosol particles were imaged and categorized according to morphological similarities into three gross morphological groups: single particles, gel particles, and halo particles. Single particles were observed between 15 and 800 nm in diameter and represent the dominating type of particles (82 %). The majority of particles appeared to be marine gels with a broad Aitken mode peaking at 70 nm and accompanied by a minor fraction of ammonium (bi)sulfate with a maximum at 170 nm in number concentration. Gel particles (11 % of all particles) were observed between 45 and 800 nm with a maximum at 154 nm in diameter. Imaging with transmission electron microscopy allowed further morphological discrimination of gel particles in "aggregate" particles, "aggregate with film" particles, and "mucus-like" particles. Halo particles were observed above 75 nm and appeared to be ammonium (bi)sulfate (59 % of halo particles), gel matter (19 %), or decomposed gel matter (22 %), which were internally mixed with sulfuric acid, methane sulfonic acid, or ammonium (bi)sulfate with a maximum at 161 nm in diameter. Elemental dispersive X-ray spectroscopy analysis of individual particles revealed a prevalence of the monovalent ions Na+/K+ for single particles and aggregate particles and of the divalent ions Ca2+/Mg2+ for aggregate with film particles and mucus-like particles. According to these results and other model studies, we propose a relationship between the availability of Na+/K+ and Ca2+/Mg2+ and the length of the biopolymer molecules participating in the formation of the three-dimensional gel networks.

Heterogeneous uptake of ammonia and dimethylamine into sulfuric and oxalic acid particles

“…This observation can be most plausibly explained by the pinning effect caused by the fast evaporation of the solvent from a droplet deposited on a substrate (Deegan et al, 1997). Similar halo formation has been described for other atmospheric particles (Hamacher-Barth et al, 2016) but we believe that this effect does not have a significant im- Figure 8. DMA-NH 3 co-uptake at DMA / NH 3 gas molar ratios of 0.5 (Table 1) pact on the general uptake observations here.…”

“…Post-reaction samples were analysed by ion chromatography (IC). R 3 N and NH 3 gas molecules and aminium ions in solution tend to adsorb on surfaces (Dawson et al, 2014;Hansen et al, 2013;Robacker and Bartelt, 1996). To ensure accuracy of the gas ratio, the system was conditioned for several hours to minimise wall losses of either one or both gases prior to the uptake experiment (see Supplement for detailed descriptions).…”

North Atlantic marine organic aerosol characterized by novel offline thermal desorption mass spectrometry approach: polysaccharides, recalcitrant material, secondary organics

“…There is some evidence for this in that stronger correlations were found between polysaccharides and inorganic ions for sub-180 nm than for submicron aerosol, in particular for K+. Previous work has shown that gel-derived aerosol particles contain different cations depending on their morphology, with smaller particles of 10s of nm diameter or their aggregates containing more Na + and K + than Mg 2+ and Ca 2+ (Hamacher-Barth et al, 2016). Larger marine aerosol particles of 0.5 -8.4 µm diameter have also been shown to have polysaccharide-like coatings that contain K + , the only inorganic cation detectable in that study .…”

The Nexus between Sea Ice and Polar Emissions of Marine Biogenic Aerosols

“…Air masses arriving in the Arctic during summer originate from sectors over the oceans with limited man-made activities (Leck and Svensson 2015), and the transport into the Arctic is slower compared to winter conditions (Stohl 2006). Summer conditions are thus much more pristine, and the aerosol shifts to smaller particle sizes (Heintzenberg et al 2015(Heintzenberg et al , 2006 with higher organic content (e.g., Hamacher-Barth et al 2016). Summer pan-Arctic crossings have shown aerosol methanesulfonic acid (MSA; an atmospheric photodegradation product of DMS) concentrations during the phytoplankton growth period to be highest in the Norwegian Sea and lowest over the central Arctic pack ice during the same time (Ye et al 2015), supporting the link between DMS emissions and ice-cover control of air-sea exchange.…”