ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-337-2005 Measurements of tropospheric NO<sub>2</sub> with an airborne multi-axis DOAS instrument Wang P. 1 Richter A. 1 Bruns M. 1 Rozanov V. V. 1 Burrows J. P. 1 Heue K.-P. 2 Wagner T. 2 Pundt I. 2 Platt U. 2 Institute of Environmental Physics, University of Bremen, Germany Institute of Environmental Physics, University of Heidelberg, Germany 07 02 2005 5 2 337 343 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/5/337/2005/acp-5-337-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/337/2005/acp-5-337-2005.pdf

The AMAXDOAS instrument is an airborne multi-axis DOAS instrument covering the spectral range from 300 to 600&nbsp;nm. During one flight of the SCIAVALUE campaign on 19 March 2003, the AMAXDOAS onboard the DLR Falcon detected tropospheric NO<sub>2</sub> over Europe under both cloudy and cloud free conditions. By combining the measurements in nadir and zenith direction, and analysing the spectra in the UV and the visible spectral region, information was derived on where the bulk of the observed NO<sub>2</sub> was located. Vertical columns of up to 5.7x10<sup>16</sup> molec&nbsp;cm<sup>-2</sup> were observed close to Frankfurt, with a distribution peaking in the boundary layer and in good agreement with surface measurements. On several occasions, strong tropospheric NO<sub>2</sub> signals were also detected when flying above clouds. The ratio of zenith and nadir measurements indicates that the NO<sub>2</sub> observed was located within the cloud, and assuming the same profile as for the cloud free situation the NO<sub>2</sub> vertical column was estimated to be 5.0x10<sup>16</sup> molec&nbsp;cm<sup>-2</sup>. The results are relevant for the retrieval of tropospheric NO<sub>2</sub> columns from space-borne instruments in cloudy situations.