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Summertime NOx measurements during the CHABLIS campaign: can source and sink estimates unravel observed diurnal cycles?

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Author(s)

  • S. J. -B. Bauguitte
  • W. J. Bloss
  • M. J. Evans
  • R. A. Salmon
  • P. S. Anderson
  • A. E. Jones
  • J. D. Lee
  • A. Saiz-Lopez
  • H. K. Roscoe
  • E. W. Wolff
  • J. M. C. Plane

Department/unit(s)

Publication details

JournalAtmospheric Chemistry and Physics
DatePublished - 2012
Issue number2
Volume12
Number of pages14
Pages (from-to)989-1002
Original languageEnglish

Abstract

NOx measurements were conducted at the Halley Research Station, coastal Antarctica, during the austral summer period 1 January-10 February 2005. A clear NOx diurnal cycle was observed with minimum concentrations close to instrumental detection limit (5 pptv) measured between 04:00-05:00 GMT. NOx concentrations peaked (24 pptv) between 19:00-20:00GMT, approximately 5 h after local solar noon. An optimised box model of NOx concentrations based on production from in-snow nitrate photolysis and chemical loss derives a mean noon emission rate of 3.48 x 10(8) molec cm(-2) s(-1), assuming a 100m boundary layer mixing height, and a relatively short NOx lifetime of similar to 6.4 h. This emission rate compares to directly measured values ranging from 2.1 to 12.6 x 10(8) molec cm(-2) s(-1) made on 3 days at the end of the study period. Calculations of the maximum rate of NO2 loss via a variety of conventional HOx and halogen oxidation processes show that the lifetime of NOx is predominantly controlled by halogen processing, namely BrNO3 and INO3 gas-phase formation and their subsequent heterogeneous uptake. Furthermore the presence of halogen oxides is shown to significantly perturb NOx concentrations by decreasing the NO/NO2 ratio. We conclude that in coastal Antarctica, the potential ozone production efficiency of NOx emitted from the snowpack is mitigated by the more rapid NOx loss due to halogen nitrate hydrolysis.

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