Atmospheric nitrogen oxides (NO and NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) at Dome C, East Antarctica, during the OPALE campaign

M M Frey,A Kukui,J Savarino,H K Roscoe,S Preunkert,M D King,J L France,M Legrand

doi:10.5194/acp-15-7859-2015

Abstract

Abstract. Mixing ratios of the atmospheric nitrogen oxides NO and NO2 were measured as part of the OPALE (Oxidant Production in Antarctic Lands &amp; Export) campaign at Dome C, East Antarctica (75.1° S, 123.3° E, 3233 m), during December 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 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 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 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, possibly indicating the existence of an unknown process contributing 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 mixing height and significant NOx emissions by surface snow (FNOx). During 23 December 2011–12 January 2012, median 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− concentrations 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.

Highlights

The nitrogen oxides NO and NO2 (NOx = NO + NO2) play a key role in the polar troposphere in determining its oxidation capacity, defined here as the sum of O3, HOx radicals, and hydrogen peroxide (H2O2)
The influence is achieved via photolysis of NO2, the only source for in situ production of tropospheric O3, through shifting HOx radical partitioning towards the hydroxyl radical (OH) via the reaction
Mixing ratios of NOx on the East Antarctic Plateau are unusually large, similar to those from the midlatitudes (Davis et al, 2008; Slusher et al, 2010; Frey et al, 2013). Such large mixing ratios of NOx were found to arise from a combination of several factors: continuous sunlight, location at the bottom of a large air drainage basin, low temperatures leading to low primary production rates of HOx radicals, significant emissions of NOx from surface snow, and a shallow boundary layer (Davis et al, 2008; Frey et al, 2013, and references therein)

Summary

Introduction

Mixing ratios of NOx on the East Antarctic Plateau are unusually large, similar to those from the midlatitudes (Davis et al, 2008; Slusher et al, 2010; Frey et al, 2013). Such large mixing ratios of NOx were found to arise from a combination of several factors: continuous sunlight, location at the bottom of a large air drainage basin, low temperatures leading to low primary production rates of HOx radicals, significant emissions of NOx from surface snow, and a shallow boundary layer (Davis et al, 2008; Frey et al, 2013, and references therein)

Methods

Results

Conclusion