2.1. Definitions
Aerosol iodine quantities are defined as in (Gómez Martín et al., 2021). Total iodine (TI) is given by the sum of total soluble iodine (TSI) and non-soluble iodine (NSI): TI = TSI + NSI. Total soluble iodine encompasses total inorganic iodine (TII = [I-] + [IO3-]) and SOI. Note that except for one recent organic speciation work (Yu et al., 2019), the only individual species reported in the majority of field measurement (Tables S1 and S2) are iodide (I-) and iodate (IO3-). SOI is determined from the TSI, I- and IO3-observations: SOI = TSI - [I-] - [IO3-]. The soluble speciation is the set of three ratios of the concentrations of I-, IO3- and SOI to TSI.
Iodine in bulk aerosol and in the fine and coarse aerosol fractions are noted respectively as Xbulk, Xfine, Xcoarse (X = TI, TSI). Particulate matter with diameterd < x μm is noted as PMx, and TI and TSI for diameter d < x μm are noted as TIx and TSIx. Usually the cut-off between fine and coarse aerosol is stablished operationally at a particle diameter of 1 μm. This reflects approximately the usual size classification of marine aerosol, characterized by the nuclei (d< 0.1 μm), the accumulation mode (0.1 μm < d< 0.6 μm) and the coarse mode (d > 0.6 μm) (Seinfeld & Pandis, 1998). PM1 encompasses the nuclei and the accumulation mode and is composed mostly of sulfate aerosol (low pH), while coarse marine aerosol consists of sea-salt aerosol produced by bubble bursting and wave breaking.