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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-866
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Oct 2018

Research article | 12 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Near-surface and path-averaged mixing ratios of NO2 derived from car DOAS zenith-sky and tower DOAS off-axis measurements in Vienna: a case study

Stefan F. Schreier1, Andreas Richter2, and John P. Burrows2 Stefan F. Schreier et al.
  • 1Institute of Meteorology, University of Natural Resources and Life Sciences, Vienna, Austria
  • 2Institute of Environmental Physics, University of Bremen, Germany

Abstract. Nitrogen dioxide (NO2), produced as a result of fossil fuel combustion, biomass burning, lightning, and soil emissions, is a key urban and rural tropospheric pollutant. In this case study, ground-based remote sensing has been coupled with the in situ network in Vienna, Austria, to investigate NO2 distributions in the planetary boundary layer. Near-surface and path-averaged NO2 mixing ratios within the metropolitan area of Vienna are estimated from car DOAS (Differential Optical Absorption Spectroscopy) zenith-sky and tower DOAS horizon observations. The latter configuration is innovative in the sense that it obtains horizontal measurements at more than hundred different azimuthal angles – within a 360° rotation taking less than half an hour. Spectral measurements were made with a DOAS instrument on nine days in April, September, October, and November 2015 in the zenith-sky mode and on five days in April and May 2016 in the off-axis mode. The analysis of tropospheric NO2 columns from the car measurements and O4 normalized NO2 path averages from the tower observations provide interesting insights into the spatial and temporal NO2 distribution over Vienna. Integrated column amounts of NO2 from both DOAS-type measurements are converted into mixing ratios by different methods. The estimation of near-surface NO2 mixing ratios from car DOAS tropospheric NO2 vertical columns is based on a linear regression analysis including mixing-height and other meteorological parameters that affect the dilution and reactivity in the planetary boundary layer – a new approach for such conversion. Path-averaged NO2 mixing ratios are calculated from tower DOAS NO2 slant column densities by taking into account topography and geometry. Overall, lap averages of near-surface NO2 mixing ratios obtained from car DOAS zenith-sky measurements, around a circuit in Vienna, are in the range of 3.8 to 26.2ppb and in good agreement with values obtained from in situ NO2 measurements for days with wind from the Southeast. Path-averaged NO2 mixing ratios at 160m above the ground as derived from the tower DOAS measurements are between 2.5 and 9ppb on two selected days with different wind conditions and pollution levels and show similar spatial distribution as seen in the car DOAS zenith-sky observations. We conclude that the application of the two methods to obtain near-surface and path-averaged NO2 mixing ratios is promising for this case study.

Stefan F. Schreier et al.
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Stefan F. Schreier et al.
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Short summary
In this case stuy, we have coupled ground-based remote sensing measurements with surface in situ measurements to investigate NO2 distributions in the planetary boundary layer in the Viennese metropolitan area. We find that the application of a novel linear regression analysis for the conversion of tropospheric NO2 vertical columns into near-surface NO2 mixing ratios is promising and thus, the method needs to be further explored and tested on satellite observations in future studies.
In this case stuy, we have coupled ground-based remote sensing measurements with surface in situ...
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