Near-Surface Refractory Black Carbon Observations in the Atmosphere and Snow in the McMurdo Dry Valleys, Antarctica, and Potential Impacts of Foehn Winds

摘要

Measurements of light-absorbing particles in the boundary layer of the high southern latitudes are scarce, particularly in the McMurdo Dry Valleys (MDV), Antarctica. During the 2013–2014 austral summer near-surface boundary layer refractory black carbon (rBC) aerosols were measured in air by a single-particle soot photometer (SP2) at multiple locations in the MDV. Near-continuous rBC atmospheric measurements were collected at Lake Hoare Camp (LH) over 2 months and for several hours at more remote locations away from established field camps. We investigated periods dominated by both upvalley and downvalley winds to explore the causes of differences in rBC concentrations and size distributions. Snow samples were also collected in a 1 m pit on a glacier near the camp. The range of concentrations rBC in snow was 0.3–1.2 ± 0.3 μg-rBC/L-H_2O, and total organic carbon was 0.3–1.4 ± 0.3 mg/L. The rBC concentrations measured in this snow pit are not sufficient to reduce surface albedo; however, there is potential for accumulation of rBC on snow and ice surfaces at low elevation throughout the MDV, which were not measured as part of this study. At LH, the average background rBC mass aerosol concentrations were 1.3 ng/m~3. rBC aerosol mass concentrations were slightly lower, 0.09–1.3 ng/m~3, at the most remote sites in the MDV. Concentration spikes as high as 200 ng/m~3 were observed at LH, associated with local activities. During a foehn wind event, the average rBC mass concentration increased to 30–50 ng/m~3. Here we show that the rBC increase could be due to resuspension of locally produced BC from generators, rocket toilets, and helicopters, which may remain on the soil surface until redistributed during high wind events. Quantification of local production and long-range atmospheric transport of rBC to the MDV is necessary for understanding the impacts of this species on regional climate.