Measuring Photodegradation of Humic Substances with a Quartz Crystal Microbalance

MINGRUI SUN, Geoffrey Smith, University of Georgia

     Abstract Number: 68
     Working Group: Aerosol Chemistry

Abstract
Formed from the oxidation of volatile organic compounds (VOCs) in the atmosphere, secondary organic aerosol (SOA) represents a large portion of global submicron-sized atmospheric organic aerosol. SOA is related to multiple processes that impact climate change. Photodegradation of SOA under solar radiation induces SOA evolution.[1] A better understanding of the extent and rate of SOA material photodegradation would lead to a better representation of SOA’s roles in climate models. In this project, standard terrestrial and aquatic Humic substances were used as surrogates for atmospheric HUmic-Like Substance (HULIS). Mass loss kinetics of the humic substances’ photodegradation under 305nm (26mW LED) and 405nm (100mW Laser) light were investigated using a quartz crystal microbalance (QCM). Humic substances were deposited on the quartz crystal through evaporation of its aqueous solution. Notable mass loss (>1% per day) was achieved with both wavelengths. Changes in the chemical properties of the humic substances upon exposure to UV light were investigated using Ultraviolet-Visible (Uv-Vis) Spectroscopy and Fourier Transform Infrared (FT-IR) Spectroscopy.

Reference:
Shrivastava, M., et al. (2017), Recent advances in understanding secondary organic aerosol: Implications for global climate forcing, Rev. Geophys., 55, 509– 559, doi:10.1002/2016RG000540.