Unprecedented radioactive pollution in Spitsbergen air – first data as of 21st century

Abstract. The present study concerned the Arctic troposphere, providing an experimental database on nuclear aerosols that has improved considerably since 1999. The activity concentrations of ²³⁸Pu, ^239+240Pu and ²⁴¹Am were determined in the surface air of Hornsund, Spitsbergen, during 2007–2021. A multivariate approach was employed, incorporating meteorological data, ⁷Be, ¹³⁷Cs, ²¹⁰Pb records and isotopic ratios, to explain the transuranium dynamics of changes and provenance. ²³⁸Pu and ^239+240Pu levels were comparable to recent observations from various locations, whereas ²⁴¹Am exhibited particularly high values, with a maximum of 354 Bq/m³ detected in 2019. The highest activity concentrations of 6.61 nBq/m³ for ²³⁸Pu and 15.51 nBq/m³ for ^239+240Pu identified in 2015 could be due to fly ash particles following wildfires in proximity to the Chernobyl zone. During the remaining period, ^239+240Pu was correlated with seasonal processes, such as local resuspension and horizontal tropospheric transport of haze layers from remote areas. Similar mechanisms likely regulated a portion of ²³⁸Pu, but to a lesser extent. Unexpected single incidents of ²³⁷Np were encountered in 2013, 2014 and 2018. Furthermore, activity ratio evaluation demonstrated a frequent occurrence of ²³⁸Pu enrichment regarding known nuclear events. Unusual elevated levels of ²⁴¹Am, ²³⁸Pu and ²³⁷Np were not associated with environmental processes; therefore, the possibility of recent anthropogenic emissions should be considered. Trajectory simulations performed in 2019 showed prominent transport pathways to the Hornsund from northern Eurasia.