MAX-DOAS detection of glyoxal during ICARTT 2004

The direct detection of glyoxal (CHOCHO), the smallest -dicarbonyl, in the open atmosphere by active dif- ferential optical absorption spectroscopy (DOAS) has re- cently been demonstrated (Volkamer et al., 2005a) and trig- gered 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 comprehensive analysis of CHOCHO by passive multi axis differential optical absorp- tion spectroscopy (MAX-DOAS). CHOCHO and NO 2 slant column measurements were conducted at the Massachusetts Institute of Technology (MIT), Cambridge, USA, and on board the research vessel Ron Brown in the Gulf of Maine as part of the International Consortium for Atmospheric Re- search on Transport and Transformation (ICARTT) 2004 campaign. For a day with nearly clear sky conditions, radia- tive transfer modeling was employed to derive diurnal CHO- CHO mixing ratios in the planetary boundary layer (PBL) for both sites. CHOCHO mixing ratios at MIT varied from 40 to 140 ppt, with peak values observed around noon. Mixing ra- tios over the Gulf of Maine were found to be up to 2.5 times larger than at MIT. The CHOCHO-to-NO2 ratio 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 methodological aspects involved with MAX- DOAS measurements of CHOCHO.