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 Burrows11Institute 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 Aeronomie (BIRA-IASB), Avenue Circulaire 3, 1180 Brussels, Belgium 6National Institute of R&D for Optoelectronics (INOE), Magurele, Street Atomistilor 409, Magurele 77125, Romania
Received: 04 Oct 2016 – Accepted for review: 16 Nov 2016 – Discussion started: 17 Nov 2016
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 Meeasurements of Aerosols an 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 100 m. The airmass 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 measured intensities at the aircraft. 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 seen 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 × 1016 molec cm−2 in the polluted city center. Validation against two co-located mobile car-DOAS measurements yields good agreement between the datasets with correlation cofficients 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 mol s−1 and 13.6 ± 8.4 mol s−1, respectively.
Meier, A. C., Schönhardt, A., Bösch, T., Richter, A., Seyler, A., Ruhtz, T., Constantin, D.-E., Shaiganfar, R., Wagner, T., Merlaud, A., Van Roozendael, M., Belegante, L., Nicolae, D., Georgescu, L., and Burrows, J. P.: High-resolution airborne imaging DOAS-measurements of NO2
above Bucharest during AROMAT, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-329, in review, 2016.