ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-8-7595-2008 High spatial resolution measurements of NO<sub>2</sub> applying Topographic Target Light scattering-Differential Optical Absorption Spectroscopy (ToTaL-DOAS) Frins E. 1 Platt U. 2 Wagner T. 3 Instituto de Física, Facultad de Ingeniería, J. Herrera y Reissig 565, 11300 Montevideo, Uruguay Institut für Umweltphysik, University of Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany Max-Planck-Institut für Chemie, Becherweg 27, 55128 Mainz, Germany 17 12 2008 8 24 7595 7601 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/8/7595/2008/acp-8-7595-2008.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/8/7595/2008/acp-8-7595-2008.pdf

Topographic Target Light scattering – Differential Optical Absorption Spectroscopy (ToTaL-DOAS), also called Target-DOAS, is a novel experimental procedure to retrieve trace gas concentrations present in the low atmosphere. Scattered sunlight (diffuse or specular) reflected from natural or artificial targets located at different distances are analyzed to retrieve the spatial distribution of the concentration of different trace gases like NO<sub>2</sub>, SO<sub>2</sub> and others. We report high spatial resolution measurements of NO<sub>2</sub> mixing ratios in the city of Montevideo (Uruguay) observing three buildings as targets with a Mini-DOAS instrument. Our instrument was 146 m, 196 m, and 280 m apart from three different buildings located along a main Avenue. We obtain temporal variation of NO<sub>2</sub> mixing ratios between 30 ppb and 65 ppb from measurements of November 2007 and mixing ratios up to 50 ppb from measurements of August and September 2008. Our measurements demonstrate that ToTaL-DOAS observations can be made over relative short distances. In polluted air masses, the retrieved absorption signal was found to be sufficiently strong to allow measurements over distances in the range of several tens of meters.

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