Spatial and Temporal Variability of Iodine in Aerosol

Abstract

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 I 2 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.

Measurement report: Indirect evidence for the controlling influence of acidity on the speciation of iodine in Atlantic aerosols

“…Yu et al (2019) recently demonstrated that addition of iodide and hydrogen peroxide (H 2 O 2 ) to a lowiodine aerosol sample generated a large number of organic iodine species. Since acoustic cavitation during ultrasonication generates H 2 O 2 and other reactive oxygen species (Kanthale et al, 2008), the result of Yu et al (2019) is further evidence that the use of ultrasonic agitation is likely to alter both inorganic and organic speciation of iodine prior to its determination. This raises the possibility that much of the published literature on I speciation in aerosols over the oceans is potentially unreliable.…”

Soluble Iodine Speciation in Marine Aerosols Across the Indian and Pacific Ocean Basins

“…Total soluble iodine (TSI) in aerosols in the MBL is characterised by geographical variability, being latitudinally and longitudinally dependent on global ocean temperature, seawater iodine content, and atmospheric ozone (Gómez Martín et al, 2021). TSI itself consists of iodide (I − ), iodate (IO 3 − ), and soluble organic iodine (SOI).…”

On the Speciation of Iodine in Marine Aerosol

“…Aerosol iodine quantities are defined as in Gómez Martín et al. ( 2021 ). TI is given by the sum of total soluble iodine (TSI) and nonsoluble iodine (NSI): TI = TSI + NSI.…”

“…We have compiled the available iodine speciation data from cruises and coastal and insular ground‐based stations with the aim of inspecting the spatial variability of the ensemble and comparing them with other global ocean and aerosol variables. For completeness, we also analyze the size distribution of total and soluble iodine, which were not specifically addressed in our previous work (Gómez Martín et al., 2021 ). The questions that we want to address in this work are as follows: which species dominates the soluble iodine speciation at different latitudes and longitudes?…”