Heterogeneous trace element deposition from an effusive volcanic plume

Effusive basaltic eruptions are an important source of volatile trace elements to the troposphere. Constraining the effects of background atmospheric conditions on the transport behavior and plume lifetimes of these elements is critical, both in the use of trace elements as proxies in the geological record, and in mitigating exposure to these elements in downwind communities. Through in-situ multi-element sampling of the Fagradalsfjall (Iceland) 2021-2022 eruption plumes we present the first direct comparison of element dispersion behavior under wet and dry atmospheric conditions. We demonstrate that the alkali metals (Na, K, Rb, Cs) are depleted up to an order of magnitude more under wet background conditions compared to elements such as Se, As, and Cd, which are instead lost preferentially in drier conditions. We propose that heterogeneous element deposition from the volcanic plume is driven by the interactions between element gas-phase speciation, water solubility of the resulting complexes, particulate size-distribution, and affinity for scavenging by larger ash particles. For volcanoes situated in regions with distinct seasonal weather patterns, the delivery of elements to the surface, and thus human exposure to potentially toxic metals such as arsenic, lead, cadmium, and selenium, could therefore vary between wet and dry conditions.