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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-812
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
11 Sep 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
The Meteorology and Chemistry of High Nitrogen Oxide Concentrations in the Stable Boundary Layer at the South Pole
William Neff1, Jim Crawford2, Marty Buhr3, John Nicovich4, Gao Chen2, and Douglas Davis4 1NOAA/ESRL Physical Sciences Division and University of Colorado Cooperative Institute for Research in Environmental Sciences, Boulder CO 80305, USA
2NASA Langley Research Center, Hampton, VA 23681, USA
3Air Quality Design, Golden, CO 80403, USA
4School of Earth and Atmospheric Science, Georgia Institute of Technology, Atlanta, GA 30332, USA
Abstract. Four summer seasons of nitrogen oxide (NO) concentrations were obtained at the South Pole during the Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program (1998 and 2000) and the Antarctic Tropospheric Chemistry Investigation (ANTCI) in (2003, 2006–7). Together, analyses of their data here provide insight into the large-to-small scale meteorology that sets the stage for high NO and the significant variability that occurs day-to-day, within seasons and year-to-year. In addition, these observations reveal the interplay between physical and chemical processes at work in the stable boundary layer of the high Antarctic plateau. We found a systematic evolution of the large-scale wind system over the ice sheet from winter to summer that controls the surface boundary layer and its effect on NO: Initially in early spring (Days 280–310) the transport of warm air and clouds over West Antarctica dominates the environment over the South Pole; In late spring (Days 310–340), of significance to NO, the winds at 300-hPa exhibit a bimodal behavior alternating between NW and SE; In early summer (Days 340–375), the flow aloft is dominated by winds from the Weddell Sea. During late spring, winds aloft from the SE are strongly associated with clear skies, shallow stable boundary layers, and light surface winds from the east: it is under these conditions that the highest NO occurs. Examination of the winds at 300 hPa from 1961 to 2013 shows that this seasonal pattern has not changed significantly although the last twenty years have seen an increasing trend in easterly surface winds at the South Pole. What has also changed is the persistence of the ozone hole, often into early summer. With lower total ozone column density and higher sun elevation, the highest actinic flux responsible for the photolysis of snow nitrate now occurs in late spring under the shallow boundary layer conditions optimum for high accumulation of NO. This may occur via the non-linear HOX-NOX chemistry proposed after the first ISCAT field programs and NOX recycling to the surface where quantum yields may be large under the low-snow-accumulation regime of the Antarctic plateau. During the 2003 field program a sodar made direct measurements of the stable boundary layer depth (BLD), a key factor in explaining the chemistry of the high NO concentrations. Because direct measurements were not available in the other years, we developed an estimator for BLD using direct observations obtained in 2003 and step-wise linear regression with meteorological data from a 22-m tower (that was tested against independent data obtained in 1993). These data were then used with assumptions about the column abundance of NO to estimate surface fluxes of NOX. These results agreed in magnitude with results at Concordia Station and confirmed significant daily, intraseasonal and interannual variability in NO and its flux from the snow surface. Finally, we found that synoptic to mesoscale eddies governed the boundary layer circulation and accumulation pathways for NO at the South Pole rather than katabatic forcing. It was the small scale features of the circulation including the transition from cloudy to clear conditions that set the stage for short-term extremes in NO whereas larger-scale features were associated with more moderate concentrations.

Citation: Neff, W., Crawford, J., Buhr, M., Nicovich, J., Chen, G., and Davis, D.: The Meteorology and Chemistry of High Nitrogen Oxide Concentrations in the Stable Boundary Layer at the South Pole, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-812, in review, 2017.
William Neff et al.
William Neff et al.
William Neff et al.

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Short summary
Our study examined the effect of the seasonal cycle in meteorology from November through December and the role of stratospheric ozone depletion on the photochemical production of nitrogen oxide (NO) from nitrate in the snow at the South Pole. We found that ozone depletion which now extends into late November- early December coincides with optimum conditions (clear skies, strong surface temperature inversions, and light winds) for high concentrations of NO to accumulate at the surface.
Our study examined the effect of the seasonal cycle in meteorology from November through...
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