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 December 2011 to January 2012. Profiles of NO_x mixing ratios of the lower 100 m of the atmosphere confirm that, in contrast to South Pole, air chemistry at Dome C is dominated by strong diurnal cycles in solar irradiance and atmospheric stability. Depth

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... of mixing ratios in firn air suggest that the upper snowpack at Dome C holds a significant reservoir of photolytically produced NO₂ and is a sink of gas phase ozone (O₃). First-time observations of BrO at Dome C suggest 2–3 pptv near the ground, with higher levels in the free troposphere. Assuming steady-state, observed mixing ratios of BrO and RO₂ radicals are too low to explain the large NO₂ : NO ratios found in ambient air. A previously not considered interference with pernitric acid (HNO₄) may explain part of this inconsistency. During 2011–2012 NO_x 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 NO_x mixing ratios arose from a combination of changes in mixing height and NO_x snow emission flux <i>F</i>_{NO_x}. During 23 December 2011–12 January 2012 median <i>F</i>_{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 <i>F</i>_{NO_x} in December 2011 was largely due to changes in snow pack source strength caused primarily by changes in NO₃^&minus; concentrations in the snow skin layer, and only to a secondary order by decrease of total column O₃ and associated increase in NO₃^&minus; photolysis rates. Systematic changes in the quantum yield of NO₃^&minus; photolysis over time may contribute to the observed <i>F</i>_{NO_x} variability.