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Volume 10, issue 5 | Copyright

Special issue: Airborne ROmanian Measurements of Aerosols and Trace gases...

Atmos. Meas. Tech., 10, 1831-1857, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 May 2017

Research article | 22 May 2017

High-resolution airborne imaging DOAS measurements of NO2 above Bucharest during AROMAT

Andreas Carlos Meier1, Anja Schönhardt1, Tim Bösch1, Andreas Richter1, André Seyler1, Thomas Ruhtz2, Daniel-Eduard Constantin3, Reza Shaiganfar4, Thomas Wagner4, Alexis Merlaud5, Michel Van Roozendael5, Livio Belegante6, Doina Nicolae6, Lucian Georgescu3, and John Philip Burrows1 Andreas Carlos Meier et al.
  • 1Institute of Environmental Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
  • 2Institute for Space Sciences, Free University of Berlin, Carl-Heinrich-Becker-Weg 6–10, 12165 Berlin, Germany
  • 3“Dunarea de Jos” University of Galati, Str. Domneasca 111, Galati 800008, Romania
  • 4Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
  • 5Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Avenue Circulaire 3, 1180 Brussels, Belgium
  • 6National Institute of R&D for Optoelectronics (INOE), Magurele, Street Atomistilor 409, Magurele 77125, Romania

Abstract. In this study we report on airborne imaging DOAS measurements of NO2 from two flights performed in Bucharest during the AROMAT campaign (Airborne ROmanian Measurements of Aerosols and Trace gases) in September 2014. These measurements were performed with the Airborne imaging Differential Optical Absorption Spectroscopy (DOAS) instrument for Measurements of Atmospheric Pollution (AirMAP) and provide nearly gapless maps of column densities of NO2 below the aircraft with a high spatial resolution of better than 100m. The air mass factors, which are needed to convert the measured differential slant column densities (dSCDs) to vertical column densities (VCDs), have a strong dependence on the surface reflectance, which has to be accounted for in the retrieval. This is especially important for measurements above urban areas, where the surface properties vary strongly. As the instrument is not radiometrically calibrated, we have developed a method to derive the surface reflectance from intensities measured by AirMAP. This method is based on radiative transfer calculation with SCIATRAN and a reference area for which the surface reflectance is known. While surface properties are clearly apparent in the NO2 dSCD results, this effect is successfully corrected for in the VCD results. Furthermore, we investigate the influence of aerosols on the retrieval for a variety of aerosol profiles that were measured in the context of the AROMAT campaigns. The results of two research flights are presented, which reveal distinct horizontal distribution patterns and strong spatial gradients of NO2 across the city. Pollution levels range from background values in the outskirts located upwind of the city to about 4 ×  1016molec cm−2 in the polluted city center. Validation against two co-located mobile car-DOAS measurements yields good agreement between the datasets, with correlation coefficients of R = 0.94 and R = 0.85, respectively. Estimations on the NOx emission rate of Bucharest for the two flights yield emission rates of 15.1±9.4 and 13.6±8.4mol s−1, respectively.

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Short summary
We present airborne remote sensing measurements of NO2 in the urban area of Bucharest. NO2 is a harmful pollutant, which is emitted in combustion processes. The measurements presented here enable the creation of maps, showing the horizontal NO2 distribution across the whole city within a relatively short time window of 1.5 h. These data provide new insight into urban pollution levels and their spatial distribution.
We present airborne remote sensing measurements of NO2 in the urban area of Bucharest. NO2 is a...