Unprecedented radioactive pollution in Spitsbergen's air – first data of the 21st century

This study investigated the Arctic troposphere, providing a comprehensive experimental database on nuclear aerosols that has significantly improved since 1999. The activity concentrations of ²³⁸Pu, ²³⁹⁺²⁴⁰Pu, and ²⁴¹Am were measured in surface air at Hornsund, Spitsbergen, from 2007–2021. A multivariate approach, incorporating meteorological data, gamma-emitter records, and isotopic ratios, was employed to explain the dynamics of change and the provenance of transuranium elements. Levels of ²³⁸Pu and ²³⁹⁺²⁴⁰Pu were found comparable to those documented over the past decades at various locations. The highest activity concentrations were 6.61 nBq m⁻³ for ²³⁸Pu and 15.5 nBq m⁻³ for ²³⁹⁺²⁴⁰Pu, observed in 2015. Although coinciding with the resuspension and atmospheric transport of radionuclides due to the 2015 wildfires near the Chernobyl zone, a direct contribution to Hornsund remains uncertain. Further data exploration revealed a correlation between ²³⁹⁺²⁴⁰Pu and seasonal processes, including local dust redistribution and horizontal tropospheric transport of haze layers from distant areas. While similar mechanisms likely regulated a portion of ²³⁸Pu, its random enrichment relative to known nuclear events was frequently detected. As a general trend, ²⁴¹Am exhibited notably high activity concentrations, reaching up to 354 nBq m⁻³ in 2019. Episodic signals of ²³⁷Np were identified in 2013, 2014, and 2018. All occurrences of ²⁴¹Am, ²³⁷Np, and outliers of ²³⁸Pu were not linked to natural processes; hence, the possibility of recent radioactive emissions should be considered. Trajectory simulations conducted for 2019 indicated prominent transport pathways to Hornsund from northern Eurasia.