Abstract
Abstract. We have measured black carbon (BC) concentrations at Syowa Station, Antarctica, since February 2005. The measured BC concentrations in 2005–2016 were corrected to equivalent BC (EBC) concentrations using Weingartner's method. Seasonal features of EBC concentrations, long-range transport from mid-latitudes to the Antarctic coast, and their origins were characterized. Results show that daily median EBC concentrations were below the detection limit (0.2 ng m−3) to 63.8 ng m−3 at Syowa Station (median, 1.8 ng m−3; mean, 2.7 ng m−3 during the measurement period of February 2005–December 2016). Although seasonal features and year-to-year variations in EBC concentrations were observed, no long-term trend of EBC concentrations was clear during our measurement period. Seasonal features of EBC concentrations showed a spring maximum during September–October at Syowa Station. To elucidate EBC transport processes, origins, and the potential source area (PSA), we compared EBC data to backward trajectory analysis and chemical transport model simulation. From comparison with backward trajectory, high EBC concentrations were found in air masses from the marine boundary layer. This finding implies that transport via the marine boundary layer was the most important transport pathway to EBC concentrations at Antarctic coasts. Some EBC was supplied to the Antarctic region by transport via the upper free troposphere. Chemical transport model simulation demonstrated that the most important origins and PSA of EBC at Syowa Station were biomass burning in South America and southern Africa. Fossil fuel combustion in South America and southern Africa also have important contributions. The absorption Ångström exponent (AAE) showed clear seasonal features with 0.5–1.0 during April–October and maximum (1.0–1.5) in December–February. The AAE features might be associated with organic aerosols and mixing states of EBC.
Highlights
Carbonaceous aerosols are major aerosols in the troposphere (e.g. Gelencsér, 2004; Gilardoni and Fuzzi, 2017)
Median equivalent BC (EBC) concentrations are used for discussion because the mean EBC concentrations can be overestimated relative to ambient EBC concentrations without local contamination when the unfilterable data derived from local contamination were present in our data screening procedures
Comparison between EBC concentrations and air mass origins identified by backward trajectory implies that EBC on the Antarctic coasts was supplied mostly by transport via the marine BL (MBL) and lower free troposphere, during winter–spring
Summary
Carbonaceous aerosols are major aerosols in the troposphere (e.g. Gelencsér, 2004; Gilardoni and Fuzzi, 2017). Considering BC outflow from South America and southern Africa and local emission from tourism, we must consider the longitudinal distribution of BC in western and eastern Antarctica to compare and elucidate BC concentrations measured at each station and transport pathway to the Antarctic. (1) geographical locations of PSA, (2) seasonality of source strength, and (3) size of aerosol particles containing BC and minerals, BC can be transported by outflow from the continents in the mid-latitudes to Antarctica. As reported by Bond et al (2013), hereinafter we use the term equivalent BC (EBC) for the corrected BC mass concentrations and the measured BC concentrations using filter-based optical techniques from earlier works. Uncertainty of the measured EBC concentrations relates to (1) stability of the optical signal, (2) flow rate control, (3) spot area, and (4) scattering and shadowing effects. When local contamination was identified in CN data within 2 h, the EBC data were removed as “locally contaminated”
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