Atmospheric nitrogen oxides (NO and NO2) at Dome C, East Antarctica, during the OPALE campaign

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Frey, M. M., Roscoe, H. K., Kukui, A., Savarino, J., France, J. L., King, M. D., Legrand, M., Preunkert, S.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Antarctic; East Antarctica; South Pole; The Antarctic; Antarc*; Antarctica; South pole
• Online Access: https://doi.org/10.5194/acp-15-7859-2015; https://www.atmos-chem-phys.net/15/7859/2015/

Mixing ratios of the atmospheric nitrogen oxides NO and NO 2 were measured as part of the OPALE (Oxidant Production in Antarctic Lands & Export) campaign at Dome C, East Antarctica (75.1° S, 123.3° E, 3233 m), during December 2011 to January 2012. Profiles of NO x mixing ratios of the lower 100 m of the atmosphere confirm that, in contrast to the South Pole, air chemistry at Dome C is strongly influenced by large diurnal cycles in solar irradiance and a sudden collapse of the atmospheric boundary layer in the early evening. Depth profiles of mixing ratios in firn air suggest that the upper snowpack at Dome C holds a significant reservoir of photolytically produced NO 2 and is a sink of gas-phase ozone (O 3 ). First-time observations of bromine oxide (BrO) at Dome C show that mixing ratios of BrO near the ground are low, certainly less than 5 pptv, with higher levels in the free troposphere. Assuming steady state, observed mixing ratios of BrO and RO 2 radicals are too low to explain the large NO 2 : NO ratios found in ambient air, possibly indicating the existence of an unknown process contributing to the atmospheric chemistry of reactive nitrogen above the Antarctic Plateau. During 2011–2012, NO x mixing ratios and flux were larger than in 2009–2010, consistent with also larger surface O 3 mixing ratios resulting from increased net O 3 production. Large NO x mixing ratios at Dome C arise from a combination of continuous sunlight, shallow mixing height and significant NO x emissions by surface snow ( F NO x ). During 23 December 2011–12 January 2012, median F NO x was twice that during the same period in 2009–2010 due to significantly larger atmospheric turbulence and a slightly stronger snowpack source. A tripling of F NO x in December 2011 was largely due to changes in snowpack source strength caused primarily by changes in NO 3 − concentrations in the snow skin layer, and only to a secondary order by decrease of total column O 3 and associated increase in NO 3 − photolysis rates. A source of uncertainty in model estimates of F NO x is the quantum yield of NO 3 − photolysis in natural snow, which may change over time as the snow ages.