Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 5 2006 10.5194/acpd-6-9459-2006 http://www.atmos-chem-phys-discuss.net/6/9459/2006/ http://www.atmos-chem-phys-discuss.net/6/9459/2006/acpd-6-9459-2006.html http://www.atmos-chem-phys-discuss.net/6/9459/2006/acpd-6-9459-2006.pdf 9459 9481 2006-09-26 MAX-DOAS detection of glyoxal during ICARTT 2004 R. Sinreich R. Volkamer F. Filsinger U. Frieß C. Kern U. Platt O. Sebastián T. Wagner Institut für Umweltphysik, Universität Heidelberg, Heidelberg, Germany Massachusetts Institute of Technology, Cambridge, MA, USA now at: University of California, San Diego, La Jolla, CA, USA now at: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany The direct detection of glyoxal (CHOCHO), the smallest &alpha;-dicarbonyl, in the open atmosphere by active differential optical absorption spectroscopy (DOAS) has recently been demonstrated (Volkamer et al., 2005a) and triggered the very recent successful detection of CHOCHO from space (Kurosu et al., 2005; Wittrock et al., 2006; Beirle et al., 2006). Here we report the first detection of CHOCHO by passive multi axis differential optical absorption spectroscopy (MAX-DOAS). CHOCHO and NO₂ slant column measurements were conducted at MIT, Cambridge, USA, and on board the research vessel Ron Brown in the Gulf of Maine as part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 campaign. For a day with nearly clear sky conditions, radiative transfer modeling was employed to derive diurnal CHOCHO mixing ratios for both sites. CHOCHO mixing ratios at MIT varied from 40 to 120 ppt, with peak values observed around noon. Mixing ratios over the Gulf of Maine were found to be up to 3 times larger than at MIT. The CHOCHO-to-NO₂ratio at MIT was <0.03, and enhancements of this ratio by up to two orders of magnitude were found over the Gulf of Maine. This paper focuses on the instrumental aspects involved with MAX-DOAS measurements of CHOCHO.