Direct Effects of Air Humidity on Dust Aerosol Production: Evidences for the Surprising Role of Electrostatic Forces

Dust aerosols are produced by wind erosion, and it is widely accepted that dust aerosols can be produced only if the wind speed exceeds a certain threshold velocity, which is largely controlled by soil moisture content. The relative humidity (RH) in the air could affect soil moisture content, thereby impacting dust production indirectly. However, it is not clear if the RH can directly change dust aerosol production. Here we simulated dust production and show that the RH does play a direct role in affecting the production of dust aerosol in a quite complicated way, which can be explained by a proposal that the RH affects both the electrostatic forces and wet-bonding forces between soil particles in opposite directions. The current formula for dust aerosol production flux does not include the direct RH effect, and this study strongly suggests that it could lead to significant errors in estimating dust production.

沙尘气溶胶由风蚀作用生成，学界普遍认为，仅当风速超过某一临界阈值时才会产生沙尘气溶胶，而该临界风速在很大程度上受土壤含水率调控。空气中的相对湿度（Relative Humidity，RH）可通过影响土壤含水率，间接对沙尘生成产生影响。然而目前尚不清楚相对湿度是否会直接影响沙尘气溶胶的生成过程。本研究通过模拟沙尘生成过程，发现相对湿度确实会以极为复杂的方式直接影响沙尘气溶胶的生成，这一现象可通过下述假说解释：相对湿度会以相反的作用方向，同时调控土壤颗粒间的静电力与湿结合力。当前用于计算沙尘气溶胶生成通量的公式并未纳入相对湿度的直接影响，本研究有力表明，该疏漏可能会在沙尘生成量估算中引入显著误差。