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

H. K. Roscoe, A. Kukui, J. Savarino, James France, Martin King, M. Legrand, S. Preunkert

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Mixing ratios of the atmospheric nitrogen oxides NO and NO2 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 De- cember 2011 to January 2012. Profiles of NOx 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 influ- enced by large diurnal cycles in solar irradiance and a sud- den 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 reser- voir of photolytically produced NO2 and is a sink of gas- phase ozone (O3). 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 lev- els in the free troposphere. Assuming steady state, observed mixing ratios of BrO and RO2 radicals are too low to ex- plain the large NO2 : NO ratios found in ambient air, possi- bly indicating the existence of an unknown process contribut- ing to the atmospheric chemistry of reactive nitrogen above the Antarctic Plateau. During 2011–2012, NOx mixing ratios and flux were larger than in 2009–2010, consistent with also larger surface O3 mixing ratios resulting from increased net O3 production. Large NOx mixing ratios at Dome C arise from a combination of continuous sunlight, shallow mix- ing height and significant NOx emissions by surface snow (FNOx ). During 23 December 2011–12 January 2012, me- dian FNOx 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 FNOx in December 2011 was largely due to changes in snowpack source strength caused primarily by changes in NO3 con- centrations in the snow skin layer, and only to a secondary order by decrease of total column O3 and associated increase in NO3 photolysis rates. A source of uncertainty in model estimates of FNOx is the quantum yield of NO3 photolysis in natural snow, which may change over time as the snow ages.
Original languageEnglish
Pages (from-to)7859-7875
Number of pages17
JournalAtmospheric Chemistry and Physics
Publication statusPublished - 17 Jul 2015

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