a The campaign labels are defined in Tables S1 and S2 and their geographical location is shown in Figure 1.
b Speciation measurements for campaign C12 are reported in this work for the first time. The campaign is described in (Gómez Martín et al., 2021)
Some aspects of data treatment are discussed in the Supplementary Text ST1. Questions related to analytical methods employed to determine iodine speciation, and in particular to potential speciation changes resulting from the use of cellulose filters and ultrasonication due to the formation of oxidants (e.g. H2O2) (Kanthale et al., 2008; Yodle & Baker, 2019) are discussed in the Supplementary Text ST2.
The fraction of TI in aerosol with d < 1 µm andd > 1 µm has only been reported in one campaign (C12). Other campaigns where the fraction of iodine in fine and coarse aerosol was measured report cascade impactor size-segregated data in several size bins (S1, S2, S4, S9 and S31). These data can be binned together for d < 1 µm and d > 1 µm to get the estimates of the distribution of TI between the coarse and fine fraction. Regarding TSI, three campaigns considered a different cut-off radius (d < 2.5 µm in campaigns C8, C9 and part of S32) and only report the soluble speciation for PM2.5.