A series of measurements over the equatorial Pacific in March 1993 showed thai the volume mixing ratios of ozone were frequently well below 10 nanomoles per mole both in the marine boundary layer (MEL) and between 10 kilometers and the tropopause. These latter unexpected results emphasize the enormous variability of tropical tropospheric ozone and hydroxyl concentrations, which determine the oxidizing efficiency of the trophosphere. They also imply a convective short circuit of marine gaseous emissions, such as dimethyl sulfide, between the MBL and the uppermost troposphere, leading, for instance, to sulfate particle formation.