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.