In this work we describe the compilation and homogenization of an
extensive dataset of aerosol iodine field observations in the period
between 1963 and 2018 and we discuss the spatial and temporal
dependences of total iodine in bulk aerosol by comparing the
observations with CAM-Chem model simulations. Total iodine in aerosol
shows a distinct latitudinal dependence, with an enhancement towards the
northern hemisphere (NH) tropics and lower values towards the poles.
This behavior, which has been predicted by atmospheric models to depend
on the global distribution of the main oceanic iodine source (which in
turn depends on the reaction of surface ozone with aqueous iodide on the
sea water-air interface, generating gas-phase I2 and
HOI), is confirmed here by field observations for the first time.
Longitudinally, there is some indication of a wave-one profile in the
Tropics, which peaks in the Atlantic and shows a minimum in the Pacific,
following the wave-one longitudinal variation of tropical tropospheric
ozone. New data from Antarctica show that the south polar seasonal
variation of iodine in aerosol mirrors that observed previously in the
Arctic, with two equinoctial maxima and the dominant maximum occurring
in spring. While no clear seasonal variability is observed in NH middle
latitudes, there is an indication of different seasonal cycles in the NH
tropical Atlantic and Pacific. A weak positive long-term trend is
observed in the tropical annual averages, which is consistent with an
enhancement of the anthropogenic ozone-driven global oceanic source of
iodine over the last 50 years.