Summertime NO sub(x) measurements during the CHABLIS campaign: can source and sink estimates unravel observed diurnal cycles?

• Published in: Atmospheric chemistry and physics discussions Vol. 9; no. 5; pp. 20371 - 20406
• Main Authors: J.-B. Bauguitte, S, Bloss, W J, Evans, MJ, Salmon, R A, Ander son, PS, Jones, A E, Lee, J D, Saiz-Lopez, A, Roscoe, H K, Wolff, E W, C Plane, JM
• Format: Journal Article
• Language: English
• Published: 29.09.2009
• Subjects: PS, Antarctica
• ISSN: 1680-7367; 1680-7375

NO sub(x) measurements were conducted at the Halley Research Station, Antarctica, during the austral summer period 1 January-10 February 2005. A clear NO sub(x) diurnal cycle was observed with minimum concentrations close to instrumental detection limit (5 pptv) measured between 04:00-05:00 GMT. NO sub(x) concentrations peaked (24 pptv) between 19:00-20:00 GMT, approximately 5 h after local solar noon. An optimised box model of NO sub(x) concentrations based on production from in-snow nitrate photolysis and chemical loss derives a mean noon emission rate of 3.4810 super(8) molecules cm super(− 2) s super(− 1), assuming a 100 m boundary layer mixing height, and a relatively short NO sub(x) lifetime of ~6.4 h. This emission rate compares to directly measured values ranging from 1.7 to 3.410 super(8) molecules cm super(− 2) s super(− 1) made on 3 days at the end of the study period. Calculations of the maximum rate of NO sub(2) loss via a variety of conventional HO sub(x) and halogen oxidation processes show that the lifetime of NO sub(x) is predominantly controlled by halogen processing, namely BrNO sub(3) and INO sub(3) gas-phase formation and their subsequent heterogeneous uptake, with a potential smaller contribution from HNO sub(4) formation and uptake. Furthermore the presence of halogen oxides is shown to significantly perturb NO sub(x) concentrations by decreasing the NO/NO sub(2) ratio. We conclude that in coastal Antarctica, the potential ozone production efficiency of NO sub(x) emitted from the snowpack is mitigated by the more rapid NO sub(x) loss due to halogen nitrate hydrolysis. These results suggest that the role of halogen oxides need to be considered when interpreting the isotopic signature of nitrate impurities held within snow and ice.