Experimental evidence of chemical differences between charged and uncharged snow during blowing snow events

In this study we tested under field conditions the hypothesis that electrical phenomena may influence chemical composition of snow. The field experiment was conducted at the Akademik Vernadsky Station within the framework of the State Program of Scientific Research of Ukraine in Antarctica during two winter seasons in 2022 and 2023, using a newly designed trap for charged snow. This instrument was constructed to selectively attract charged snow particles from the blowing-snow flux and was deployed during blowing snow events The experiments were performed in winter to ensure that chemical modifications were not affected by photochemical reactions. A similar field experiment was conducted in the Arctic at Ny-Ålesund, Svalbard. Here, we focus on the chemical composition of the snow samples collected by the trap, which were analyzed using ion chromatography and compared with the composition of the background blowing snow.

We found that samples of charged snow were significantly more concentrated than background snow, which is attributed to the sublimation during conditions of blowing snow events. When the measured ion concentrations were compared with the expected concentration ranges and ratios characteristic of sea salt, the charged snow samples were, however, depleted in chloride, with this difference far exceeding the measurement uncertainty. The dependence of chloride “losses” on the fraction of sublimated water indicated a strong change and revealed the presence of a threshold at approximately 80 % sublimated water, beyond which these losses—interpreted as emissions to the atmosphere—increased sharply. Products of chlorine free-radical reactions in the atmosphere have been reported by numerous authors; however, the mechanism responsible for initiating these reactions remains uncertain. The present experiment provides evidence that the charging of snow may serve as such a triggering process. The presence of a similar threshold at 70–80 % sublimated water, after which ion losses increase sharply, was also observed for Br⁻, SO₄²⁻, and Mg²⁺. However, the presence of local sources renders these relationships less significant. The change in the composition at such high sublimation fractions may indicate emission of these ions due to overcoming of the Rayleigh limit indicating that electrical charging affects chemical processes in snow.

In contrast, the experiments conducted in the coastal marine environment at Ny-Alesund indicate that ion ratios characteristic of sea salt were preserved in the charged snow samples, demonstrating that no or only limited chemical transformations took place. The presence of sea ice appears to be critical for the manifestation of chemical effects. When sea ice is present, snow particle charging during blizzards occurs primarily due to frictional and sublimation-driven processes. In the absence of an ice surface, charging is most likely driven by the sorption of marine aerosols maintaining the expected sea salt ratios in the charged snow.