Properties of Surfactants in Size-Resolved Atmospheric Aerosol Particles

AMANDA FROSSARD, Tret Burdette, Rachel Bramblett, Kathryn Zimmermann, University of Georgia

     Abstract Number: 186
     Working Group: Aerosol Chemistry

Abstract
Surfactants are a class of organic molecules that significantly reduce surface tension at an interface. In atmospheric aerosol particles, surfactants can affect the hygroscopicity of the particles as well as their surface tension and ability to act as cloud condensation nuclei. In this study, we investigate the sources and properties of surfactants in atmospheric aerosol particles collected at Skidaway Institute of Oceanography in summer 2018. Particles were collected in ten size ranges, and organic compounds were extracted from the particles using two solid phase extractions. The major ions in the particles were measured using ion chromatography. The extracted organic fractions were characterized with high resolution time of flight mass spectrometry and tensiometry. During this study, particles were collected from three air mass source regions: Marine Influenced, Mixed, and Continental Influenced. Here, we show that the signatures of the organic extracts as well as their surface tensions vary as a function of particle size and air mass source regions. Across all particle types, the ratio of hydrogen to carbon (H/C) was higher in the submicron particles compared to the supermicron particles, indicating different organic species in the smaller particles. The surface tension minimums were also lower in the submicron particles, demonstrating stronger or higher concentrations of surfactants in the submicron particles. Chemical formulas were identified to be surfactant-like based on their relative ratios of hydrogen, carbon, oxygen, sulfur, and nitrogen. The fraction of surfactant-like formulas was negatively correlated with minimum surface tensions, demonstrating that as the surfactant fraction increased, the surface tension decreased. Additionally, formulas identified as fatty acids had longer carbon chain lengths in the Marine Influenced particles (18) compared to the Mixed (15) and Continental Influenced particles (9), which may indicate different sources of fatty acids or aging in the atmosphere that breaks down the fatty acid carbon chains.