5. Conclusions
There are some uncertainties regarding the different analytical methods employed in the determination of iodine speciation in aerosol (see supplementary text ST2 and (Yodle & Baker, 2019)), and we recommend that future work considers carefully the problems associated with the combination of cellulose filters and long time (and/or high power) ultrasonic extraction. However, the correspondence between the spatial trends of ocean productivity variables and the SOI fraction in marine aerosol determined from the global iodine speciation dataset compiled in this work, and the correlations between iodine speciation ratios and major ions concurrently measured in seven cruises indicate that the two acidity regimes and the availability of organics are major controlling factors of the iodide-iodate-SOI variability, as summarized in the chemical scheme in Figure 7. Future laboratory and modelling work needs to address the underlying chemical and photochemical reactions of this system, especially regarding the reactions between DOM and HOI and the photochemical processes linking SOI and iodide.