# Chemical Speciation of Antarctic Atmospheric Depositions
## 4 Conclusions  
The main ionic components were quantified in atmospheric depositions collected at eight sites located in Victoria Land during the Antarctic summer 2017-2018. The main inorganic cations in particulate matter aqueous extracts are represented by alkali and alkaline earth ions, and ammonium. The correlations between some components' concentrations suggest that the marine aerosol strongly affected the composition of the atmospheric depositions, as expected by the location of the sites. Moreover, there was a peculiarity in samples from Edmonson Point (D3), which were characterized by high concentrations of ammonium, acetate, formate, and zinc, probably due to the presence of an Adelie penguin rookery near the sampling site. A chemical model, based on the interaction between the main components, was proposed and applied to the samples to identify the main species occurring in atmospheric depositions. It was possible to draw the species distribution diagrams as a function of pH, and to foresee the effect of an increase in the concentration level of all the solution components, which simulates what could happen when the particles act as cloud condensation nuclei (CCN) in the atmosphere and, therefore, a thin water film covers the atmospheric particles in the process. Among transition metals, only Cu, Fe, Mn, and Zn were present in significant concentrations. The speciation study showed that most cations occurred as aquoions over the whole pH range, except for Fe that occurred predominantly as hydrolytic forms. The anions detected in the aqueous extract had a scarce influence on element speciation, due to their low concentrations. The roles of inorganic anions such as chloride, sulfate and hydrogen phosphate only became important when increasing the concentrations of the components by a factor >100, while the presence of organic acids such as acetate and formate gained significance only for samples where concentrations were higher than \(10^{-5}\) mol L\({}^{-1}\). As mentioned before, the results presented here are a first approximation of the chemical speciation of the real samples, because the formation constants used here are defined at 25 \({}^{\circ}\)C, while temperatures in the coastal Antarctic area are much lower even during summer, when water anyway occurs in the liquid phase on deliquescent particles. Still, we could identify the chemical equilibria that mostly affect the chemical system. First of all, the hydrolytic species of the cations play a key role such as, most notably, in the case of Fe(III). Furthermore, sulfate is the inorganic anion mostly involved in the formation of complexes, while organic acids would be relevant only for some samples. Future studies will need to tackle the measurement of the formation constants of these species, together with the related protonation constants of the ligands, at low temperatures and at different ionic strengths, to improve the modeling capacity. The results of such studies will enable researchers to gain insight into the behavior of metals in wet depositions, which is fundamental knowledge to drive atmospheric photochemistry studies and to model biogeochemical cycles of metal cations. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app12094438/s1](https://www.mdpi.com/article/10.3390/app12094438/s1)]([https://www.mdpi.com/article/10.3390/app12094438/s1](https://www.mdpi.com/article/10.3390/app12094438/s1)). Conceptualization, S.B. ([PERSON]), M.M. ([PERSON]), D.V. and S.I. ; methodology, S.B. ([PERSON]), S.B. ([PERSON]), S.I., M.M. ([PERSON]) and D.V. ; software and formal analysis, S.B. ([PERSON]); investigation, S.B. ([PERSON]), E.C. and S.I. ; resources, D.V., M.M. ([PERSON]), A.A. and C.T. ; data curation, S.B. ([PERSON]), M.M. ([PERSON]), E.C. and M.M. ([PERSON]); writing--original draft preparation, S.B. ([PERSON]) and S.B. ([PERSON]); writing--review and editing, S.B. ([PERSON]), S.B. ([PERSON]), O.A., D.V. and S.I. ; visualization, [PERSON] ([PERSON]) and M.M.