Chlorine Oxyacids Potentially Contribute to Arctic Aerosol Formation

To understand Arctic amplification, it is necessary to understand both the direct and indirect aerosol effect. Especially the indirect aerosol effect is important, due to the low background level of cloud condensation nuclei in the Arctic. Previous studies have shown how iodine oxyacids can contribute to the formation of aerosols in marine and polar areas, and we speculate that chlorine oxyacids, if present, could also contribute to particle formation. Recent measurements have observed the presence of chloric (CA) and perchloric acid (PA) in significant concentrations in the Arctic. Using quantum chemical methods, we have studied the (acid)_0–2(base)_0–2 clusters, where the acid denotes CA, PA, or sulfuric acid (SA) and the base denotes ammonia, methylamine, dimethylamine, or trimethylamine. This allowed us to simulate the cluster formation potential of the chemical species. We found PA to have a high nucleation potential but, due to low concentrations, should only be present as a minor constituent of nucleating clusters. However, at low temperatures during high concentration events, it can become a substantial additional contribution to SA-driven nucleation. Therefore, further measurements and studies of larger multicomponent clusters should be pursued in order to constrain the potential contribution of PA to Arctic nucleation.