The lifetime of charged dust in the atmosphere

Wind-blown dust plays a critical role in numerous geophysical and biological systems, yet current models fail to explain the transport of coarse-mode particles (>5 mu m) to great distances from their sources. For particles larger than a few microns, electrostatic effects have been invoked to account for longer-than-predicted atmospheric residence times. Although much effort has focused on elucidating the charging processes, comparatively little effort has been expended understanding the stability of charge on particles once electrified. Overall, electrostatic-driven transport requires that charge remain present on particles for days to weeks. Here, we present a set of experiments designed to explore the longevity of electrostatic charge on levitated airborne particles after a single charging event. Using an acoustic levitator, we measured the charge on particles of different material compositions suspended in atmospheric conditions for long periods of time. In dry environments, the total charge on particles decayed in over 1week. The decay timescale decreased to days in humid environments. These results were independent of particle material and charge polarity. However, exposure to UV radiation could both increase and decrease the decay time depending on polarity. Our work suggests that the rate of charge decay on airborne particles is solely determined by ion capture from the air. Furthermore, using a one-dimensional sedimentation model, we predict that atmospheric dust of order 10 mu m will experience the largest change in residence time due to electrostatic forces.

Automated summary

Wind-blown dust plays an important role in various systems, but current models cannot explain the long-distance transport of large particles. This study investigates the longevity of electrostatic charge on airborne particles and finds that the charge decayed over time, lasting for more than a week in dry environments and several days in humid environments. The decay rate was independent of particle material and charge polarity, but UV radiation could affect the decay time. The findings also predict that atmospheric dust of around 10 μm will experience the greatest change in residence time due to electrostatic forces.