2.2. Description and treatment of datasets
In this work we keep the same campaign labels used in our previous
publication on total iodine (Gómez Martín et al., 2021), for
consistency. Tables S1 and S2 list respectively the 16 cruises (C#) and
12 coastal ground-based (S#) campaigns where aerosol iodine
measurements have been carried out. Iodine speciation measurements are
heterogeneous and do not always cover the same species or group of
species. The data can be classified in five groups according to the
iodine species reported and their size segregation in fine and coarse
aerosol, as shown in Tables S1 and S2, and summarized in Table 1. For
some of the cruises where the size distribution of soluble iodine
species was reported (C4, C6, C10, C14, C17, C19 and C20) there are also
measurements of major ions (MI) available (Allan et al., 2009; Baker et
al., 2006, 2007; Droste et al., 2021; Martino et al., 2014; Powell et
al., 2015), which are used in this work to investigate potential
relationships with the iodine observations. MI observations include
Na+, NH4+,
Mg2+, Ca2+, K+,
Cl-, NO3-,
SO42-, oxalate
(C2O4-2),
Br- and methanesulfonate
(CH3SO3-), and derived
quantities such as non-sea-salt (nss) K+,
Ca2+ and SO42- as
defined in (Baker & Yodle, 2021). Na+ is the sea-salt
tracer. The precursor of
C2O4-2, oxalic acid is
emitted from fossil fuel combustion, biomass burning and biogenic
activity, and it is also an oxidation product of both biogenic
(isoprene) and of anthropogenic (e.g. cycloalkanes) emissions (Zhou et
al., 2015). Combustion of fossil fuel and biomass are a source of
NO3-, while
NH4+ is linked to ammonia emissions
from agriculture, although it also has background marine sources. The
non-sea-salt ions are tracers of biomass burning, mineral dust and
sulfur emissions (volcanic, biogenic or anthropogenic), respectively
(Martino et al., 2014).
CH3SO3- and
nss_SO4- are oxidation products of
marine biogenic DMS (Andreae et al., 1999), but can also be linked to
biomass burning, and agricultural and urban emissions.
Table 1. Summary of available field observations of iodine
speciation in aerosol