Comment on acp-2021-417

doi:10.5194/acp-2021-417-rc1

Abstract

Self-charging of radioactive uranium oxide particles was measured by comparing the electrostatic surface-charge characteristics of the uranium particles to various airborne dust particulates. Though radioactive aerosols can gain charge through various decay mechanisms, researchers have traditionally assumed that the radioactive aerosols do not carry any additional charge relative to other atmospheric dust particles as a consequence of charge neutralization over time. In this work, we evaluate this assumption by directly examining the surface charge and charge density on airborne uranium oxide particles and then comparing those characteristics with charging of other natural and engineered airborne dust particles. Based on electric field–assisted particle levitation in air, the surface charge, charge distribution as a function of particle size, and surface charge density were determined for uranium oxide aerosols (< 1 µm) and other nonradioactive dusts, including urban dust, Arizona desert dust, hydrophilic and hydrophobic silica nanoparticles, and graphene oxide powders. Of these dusts, uranium oxide aerosols exhibited the highest surface change density. Additionally, a self-charging model was employed to predict average charge gained from radioactive decay as a function of time. The experimental and theoretical results suggest that radioactive self-charging likely occurs on airborne particles containing radionuclides and may potentially affect the transport of radioactive particles in the atmosphere.

Highlights

Considering the substantial public health risks and environmental damage that could arise from the deposition of debris from unwanted nuclear events, the development of tools that can accurately predict the transport of such a debris is of great importance (Pöllänen et al 1997, Yamauchi 2012, Draxler et al, 2015, Yoshikane et al, 2016)
Even for nonradioactive particles, the electrostatic forces acting on airborne particulates play a significant role in the transport of dusts that are lofted into the atmosphere and transported thousands of kilometers from their point of origin (Kok et al, 2006; Kok et al, 2008)
In this formula, vf is the velocity of the particle in free fall (m/s), vr is the upward velocity of the particle in a known electric field, g is the gravitational acceleration (m/s2), r is the particle density, d is the distance separating the plates (m), V is the potential difference across the plates (V), a is the particle’s radius (m), b is a constant equal to 8.2 × 10-3 Pa

Summary

Introduction

Considering the substantial public health risks and environmental damage that could arise from the deposition of debris from unwanted nuclear events, the development of tools that can accurately predict the transport of such a debris is of great importance (Pöllänen et al 1997, Yamauchi 2012, Draxler et al, 2015, Yoshikane et al, 2016). To effectively predict the transport of radioactive particles in the atmosphere, one must first obtain a reliable estimation of the aerosol’s surface charge characteristics (ApSimon et al, 1989; Lee et al, 1995; Pöllänen et al, 1997; Andrews et al, 2020). Heavy charging of airborne dusts during dust storms is well documented in the literature; some storms develop an electrical field in excess of 100 kV/m (Gensdarmes et al 2001). These electric fields arise from contact charging of wind-blown dust particles as they collide with one another and transfer charge though the triboelectric effect.

Methods

Results

Conclusion