Humidity-Induced Changes in the Optical Properties of Dust Particles

KYLE GORKOWSKI, Rachael Dal Porto, Christopher Cappa, Ryan Farley, Qi Zhang, Abu Sayeed Md Shawon, Jordan Spencer, James E. Lee, Katherine Benedict, Manvendra Dubey, Allison Aiken, Los Alamos National Laboratory

     Abstract Number: 224
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
Dust is a ubiquitous atmospheric particle that has significant impacts on climate, air quality, and human health. While the optical properties of dust, such as absorption coefficients, have been studied extensively, the influence of humidity on these properties is poorly measured despite dust particles often encountering varying levels of atmospheric moisture.

In this study, we report on new field measurements taken in Houston during the DOE ARM’s TRACER-CAT campaign in July 2022. We investigated the effects of humidity on the optical properties of dust using a combination of field measurements and numerical simulations. We used a custom-built instrument, the dual-channel Humidified-Cavity-Attenuated Phase Shift-Single Scattering Albedo Particulate Matter Monitor (H-CAPS-PM), to measure the optical properties of dust particles under controlled levels of relative humidity. Our results show an increase in aerosol scattering and extinction, as well as an increase in single scatter albedo, with increasing humidity. However, the absorption increase with humidity was found to be variable.

To assess our measurements, we also conducted simulations using the Mie theory with modified effective refractive indexes to include the effect of water uptake by dust particles. The simulations confirmed the changes in the optical properties of dust particles due to humidity and showed the importance of incorporating these effects into atmospheric models.

Our findings have important implications for understanding the role of dust in atmospheric processes and climate change. By incorporating the effects of humidity on dust optical properties into atmospheric models, we can improve our predictions of dust radiative forcing and the resulting impacts on regional and global climate.