Full latitudinal marine atmospheric measurements of iodine monoxide

Iodine compounds destroy ozone (O3) in the global troposphere and form new aerosols, thereby affecting the global radiative balance. However, few reports have described the latitudinal distribution of atmospheric iodine compounds. This work reports iodine monoxide (IO) measurements over unprecedented sampling areas from Arctic to the Southern Hemisphere and spanning sea surface temperatures (SSTs) of approximately 0 °C to 31.5 °C. The highest IO concentrations were observed over the Western Pacific warm pool (WPWP), where O3 minima were also measured. There, negative correlation was found between O3 and IO mixing ratios at extremely low O3 concentrations. This correlation is not explained readily by the “O3-dependent” oceanic fluxes of photolabile inorganic iodine compounds, the dominant source in recent global-scale chemistry-transport models representing iodine chemistry, and rather implies that “O3-independent” pathways can be similarly important in the WPWP. The O3-independent fluxes result in a 15 % greater O3 loss than that estimated for O3-dependent processes alone. The daily O3 loss rate related to iodine over the WPWP is as high as approximately 2 ppbv despite low O3 concentrations of ~10 ppbv, with the loss being up to 100 % greater than that without iodine. This finding suggests that warming SST driven by climate change may affect the marine atmospheric chemical balance through iodine–ozone chemistry.