Figure 5 . Absolute correlation hierarchical clustering
dendrograms for iodine speciation and major ion (MI) variables. Top
panel: fine (PM1) aerosol. Bottom panel: coarse aerosol.
The vertical dashed line indicates the distance (R > 0.4)
chosen for the definition of clusters, which are identified by different
colors.
In fine aerosol, the SOI fraction is positively correlated to some ions
within the marine emissions cluster, as well as to Cl-and C2O42‑, for the
coastal data subset. For the open ocean data subset, the SOI fraction is
anticorrelated to Na+, and positively correlated to
C2O42‑, while the
IO3- fraction is also significantly
anticorrelated to
C2O42‑. Note that
C2O42‑ ions are
associated to different clusters in the two subsets (Figure S7-S8),
although both are linked to biomass burning and agricultural emissions
(the nitrogen-containing ions cluster for coastal fine aerosol and the
nss_K+ cluster in the open ocean).