Summertime NO<sub>x</sub> measurements during the CHABLIS campaign: can source and sink estimates unravel observed diurnal cycles?
NO<sub>x</sub> measurements were conducted at the Halley Research Station, coastal Antarctica, during the austral summer period 1 January–10 February 2005. A clear NO<sub>x</sub> diurnal cycle was observed with minimum concentrations close to instrumental detection limit (5 p...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2012-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/12/989/2012/acp-12-989-2012.pdf |
| Summary: | NO<sub>x</sub> measurements were conducted at the Halley Research Station, coastal Antarctica, during the austral summer period 1 January–10 February 2005. A clear NO<sub>x</sub> diurnal cycle was observed with minimum concentrations close to instrumental detection limit (5 pptv) measured between 04:00–05:00 GMT. NO<sub>x</sub> 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</sub> concentrations based on production from in-snow nitrate photolysis and chemical loss derives a mean noon emission rate of 3.48 × 10<sup>8</sup> molec cm<sup>−2</sup> s<sup>−1</sup>, assuming a 100 m boundary layer mixing height, and a relatively short NO<sub>x</sub> lifetime of ~6.4 h. This emission rate compares to directly measured values ranging from 2.1 to 12.6 × 10<sup>8</sup> molec cm<sup>−2</sup> s<sup>−1</sup> made on 3 days at the end of the study period. Calculations of the maximum rate of NO<sub>2</sub> loss via a variety of conventional HO<sub>x</sub> and halogen oxidation processes show that the lifetime of NO<sub>x</sub> is predominantly controlled by halogen processing, namely BrNO<sub>3</sub> and INO<sub>3</sub> gas-phase formation and their subsequent heterogeneous uptake. Furthermore the presence of halogen oxides is shown to significantly perturb NO<sub>x</sub> concentrations by decreasing the NO/NO<sub>2</sub> ratio. We conclude that in coastal Antarctica, the potential ozone production efficiency of NO<sub>x</sub> emitted from the snowpack is mitigated by the more rapid NO<sub>x</sub> loss due to halogen nitrate hydrolysis. |
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| ISSN: | 1680-7316 1680-7324 |