Scavenging of atmospheric ions and aerosols by drifting snow in Antarctica

Measurements of the small,intermediate, and large ion concentrations and the airearth current density along with simultaneous measurements of the concentration and size-distribution of aerosol particles in the size ranges 4.4 to 163 nm and 0.5 to 20 micrometer diameters are reported for a drifting snow period after the occurrence of a blizzard at a coastal station, Maitri, Antarctica. Ion concentrations of all categories and the airearth current simultaneously decrease by approximately an order of magnitude as the wind speed increases from 5 to 10 meter per sec. The rate of decrease is the highest for large ions, lowest for small ions and in between the two for intermediate ions. Total aerosol number concentration decreases in the 4.4 to 163 nm size range but increases in 0.5 to 20 micrmetr size range with wind speed. Size distribution of the nanometer particles show a dominant maximum at 30 nm diameter throughout the period of observations and the height of the maximum decreases with wind speed. However, larger particles show a maximum at 0.7 micrometer diameter but the height of the maximum increases with increasing wind speed. The results are explained in terms of scavenging of atmospheric ions and aerosols by the drifting snow particles.

💡 Research Summary

This study investigates how drifting snow—loose snow particles mobilized by wind after a blizzard—affects atmospheric ions and aerosol populations at the coastal Antarctic research station Maitri. Using a suite of instruments, the authors simultaneously measured concentrations of small (diameter < 1.5 nm), intermediate (1.5–10 nm), and large ( > 10 nm) ions, the vertical air‑earth current density, and aerosol size distributions in two distinct ranges: nanometer‑scale particles (4.4–163 nm) and micrometer‑scale particles (0.5–20 µm). Wind speed was monitored continuously, and data were analyzed for periods when the wind increased from roughly 5 m s⁻¹ to 10 m s⁻¹ during a drifting‑snow episode.

The key findings are: (1) All ion categories and the air‑earth current density drop by about an order of magnitude as wind speed doubles. The decline is steepest for large ions, moderate for intermediate ions, and shallowest for small ions, indicating size‑dependent scavenging efficiency. (2) In the nanometer range, total aerosol number concentration declines with stronger wind, and the dominant size‑distribution peak at ~30 nm diminishes in height. (3) Conversely, in the micrometer range, total particle concentration rises, with a pronounced peak near 0.7 µm that becomes more prominent as wind speed increases.

These observations are interpreted through the lens of scavenging (or removal) of charged particles by drifting snow. Large ions and larger aerosol particles have higher collision cross‑sections with snow grains, leading to rapid removal from the air column. Small ions, being more mobile, experience fewer collisions and thus exhibit a milder decrease. For nanometer‑scale aerosols, the reduction of the 30 nm mode suggests that snow grains either capture these particles directly or cause them to recombine and settle, thereby depleting the atmospheric pool. The growth of the 0.7 µm mode is attributed to the snow particles themselves acting as a source of coarse aerosol: as snow grains tumble, they fragment, erode, or aggregate, generating new particles in the sub‑micron to micrometer size range.

The study provides quantitative evidence that drifting snow can significantly modulate atmospheric electrical properties and aerosol populations in polar environments. The simultaneous decline of ion concentrations and air‑earth current density underscores the need to incorporate snow‑particle scavenging processes into atmospheric electricity models for high‑latitude regions. Moreover, the contrasting responses of nanometer‑ versus micrometer‑scale aerosols highlight the importance of particle size and charge in governing removal mechanisms. These insights have broader implications for polar climate modeling, aerosol‑cloud interaction studies, and the interpretation of ion‑based atmospheric measurements in environments where strong winds and snow are common.