Airborne observations of DMSO, DMS, and OH at marine tropical latitudes

This paper reports the first simultaneous fast-time resolution measurements of dimethylsulfide (DMS), dimethylsulfoxide (DMSO), and the hydroxyl radic al (OH) at marine tropical latitudes. These observations were recorded duri ng the PEM-Tropics B field program on NASA's P-3B aircraft. The observation s of DMSO, using a Selected Ion Chemical Ionization Mass Spectrometry (SICI MS) technique, are of particular significance. They have revealed two uniqu e findings: 1) average midday-tropical levels of DMSO are significantly hig her than those predicted from current models when constrained by observed D MS and OH levels (e.g., 10 pptv versus 1 to 3 pptv); and 2) DMSO concentrat ion profiles are significantly out-of-phase with model predictions, maximum values being seen under near dark conditions and minimum values being obse rved at midday. Although no simple explanation has yet been found for these unusual results, the fact that no evidence points to a problem in the meas urements suggests that others may exist. Clearly, if the observations are c orrect, they indicate that at least for tropical upwelling regions the atmo spheric sulfur budget may need to be adjusted to accommodate additional sou rces of DMSO.