Abstract
Abstract. Observations of the organic components of the natural aerosol are scarce in Antarctica, which limits our understanding of natural aerosols and their connection to seasonal and spatial patterns of cloud albedo in the region. From November 2015 to December 2016, the ARM West Antarctic Radiation Experiment (AWARE) measured submicron aerosol properties near McMurdo Station at the southern tip of Ross Island. Submicron organic mass (OM), particle number, and cloud condensation nuclei concentrations were higher in summer than other seasons. The measurements included a range of compositions and concentrations that likely reflected both local anthropogenic emissions and natural background sources. We isolated the natural organic components by separating a natural factor and a local combustion factor. The natural OM was 150 times higher in summer than in winter. The local anthropogenic emissions were not hygroscopic and had little contribution to the CCN concentrations. Natural sources that included marine sea spray and seabird emissions contributed 56 % OM in summer but only 3 % in winter. The natural OM had high hydroxyl group fraction (55 %), 6 % alkane, and 6 % amine group mass, consistent with marine organic composition. In addition, the Fourier transform infrared (FTIR) spectra showed the natural sources of organic aerosol were characterized by amide group absorption, which may be from seabird populations. Carboxylic acid group contributions were high in summer and associated with natural sources, likely forming by secondary reactions.
Highlights
West Antarctica is one of the most rapidly warming regions on Earth (Bromwich et al, 2013), which has potential impacts for the melting of the Antarctic ice sheets and consequent sea level rise (Steig et al, 2009; Lambeck et al, 2002)
Ambient aerosols contribute substantially to the radiation balance (IPCC, 2013), but little is known about the sign and magnitude of their contribution in Antarctica because of the lack of measurements of their abundance, composition, and sources
The ARM West Antarctic Radiation Experiment (AWARE) aerosol measurements were collected from 23 November 2015 to 29 December 2016 at the Cosray site on the eastern edge of McMurdo Station (77.85◦ S, 166.66◦ E), which is located on the southern tip of Ross Island in Antarctica
Summary
West Antarctica is one of the most rapidly warming regions on Earth (Bromwich et al, 2013), which has potential impacts for the melting of the Antarctic ice sheets and consequent sea level rise (Steig et al, 2009; Lambeck et al, 2002). This low winter and high summer seasonal difference has been observed at coastal Antarctic sites, but the average concentrations were typically higher, with summertime concentrations ranging from 300 to 2000 cm−3 and wintertime concentrations from 10 to 200 cm−3 (Kim et al, 2017; Gras, 1993) Consistent with this seasonal difference in particle number concentrations, most summertime non-sea salt sulfate mass concentrations were at least 5 times higher than winter concentrations (Jourdain and Legrand, 2002; Weller and Wagenbach, 2007; Udisti et al, 2012; Legrand et al, 2017a; Asmi et al, 2018), likely because of the contributions from biogenic DMS emissions from the surrounding Southern Ocean. Seasonal patterns of natural marine and coastal-sourced organic aerosol are identified from the functional groups after separation of local emissions
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