Vibrational Spectroscopy Insights Into Multiphase Chemistry and Evolution of Atmospheric Aerosols

Atmospheric aerosols have substantial impacts on human health and global climate, making it critical to understand how aerosol change and evolve during atmospheric lifetimes ranging from hours to weeks. Aerosols are complex environments where low water content, variable acidity, and organic species lead to difficult to predict multiphase chemistry. Probing individual aerosol particles at ambient temperature and pressure is critical to avoid modification under vacuum, which has led our group and others to focus on the application of vibrational spectroscopy to studying aerosol systems. As the aerosols with the longest atmospheric lifetimes range from 100-1000 nm, we use a combination of atomic force microscopy coupled with photothermal infrared spectroscopy (AFM-PTIR) and optical photothermal infrared spectroscopy (O-PTIR) coupled with simultaneous Raman microspectroscopy to probe aerosol particles in the laboratory and ambient atmosphere. This presentation will focus on how we have used these methods to monitor how secondary organic aerosol (SOA) forms under a range of acidity and relative humidity conditions and how that changes physicochemical properties like glass transition temperature and viscosity in individual particles. We find that the formation conditions play a critical role in determining the properties of SOA and their ultimate impacts on climate and health.