Effects on local atmospheric environment of volcanic ash from Sakurajima volcano, inferred from atmospheric deposition of Potassium-40 at Kagoshima City, Japan.

In this study, we statistically demonstrated that an anomalous high of ⁴⁰ K fallout in the atmospheric fallout in Kagoshima City is caused by heavy ashfall associated with eruptions of Sakurajima volcano. Sakurajima is one of the most active volcanoes in Japan, and its repeated explosive eruptions cause large amounts of ash to fall on Kagoshima City. The fallout of crust-derived natural radionuclides, ⁴⁰ K, ²¹² Pb, and ²¹⁴ Bi, from the atmosphere in Kagoshima City showed a significant correlation with the number of eruptions of Sakurajima volcano and the amount of ashfall in Kagoshima City. In contrast, no significant correlation was found between ⁴⁰ K and ⁷ Be fallout. The ⁴⁰ K fallout indicates that almost all of the atmospheric fallout in Kagoshima City is composed of volcanic ash particles. The contribution from mineral and sea salt particles other than volcanic ash is minimal. The mass balance of the observed ⁴⁰ K fallout, ashfall, and atmospheric fallout yield indicates that there is a significant amount of volcanic ash deposition that is not accounted for as ashfall. In most cases, the ash deposition observed as ashfall is only 30-70 wt% of the total deposition collected as atmospheric fallout samples, and the remaining portion is fine-grained and behaves as suspended volcanic ash particles, which significantly impact the atmospheric environment.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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