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).