A continuous section of surface ozone concentration in the eastern equatorial and southern tropical Atlantic shows maximum values (30--48 ppbV) in the ITCZ with low uniform values (13--15 ppbV) in the southeast trades. The high values are associated with mesoscale downdrafts in the convergence region. The southerly data show diurnal variations with night-time maxima the amplitude of which increases landwards. These are probably caused by atmospheric cooling over the warm ocean.