Determining Glass Transition Temperatures of Individual Isoprene-Derived Secondary Organic Aerosol Particles
KATHERINE KOLOZSVARI, Yao Xiao, Alison Fankhauser, Jin Yan, Madeline Cooke, Cara Waters, Rebecca Parham, N. Cazimir Armstrong, Zhenfa Zhang, Avram Gold, Jason Surratt, Andrew Ault,
University of Michigan Abstract Number: 622
Working Group: Instrumentation and Methods
AbstractThe ability of an atmospheric aerosol particle to take up water or to participate in heterogeneous reactions is highly influenced by its phase state – solid, semi-solid, or liquid. The changes in phase state can be predicted by glass transition temperature (T
g), as particles at temperatures below their T
g will show solid properties, while increasing the temperature above their T
g will allow for semi-solid and eventually liquid properties. Historically, measurements of the T
g of bulk materials have been studied in order to model the phase states of aerosols in the atmosphere; however, these methods only permit an estimation of aerosol Tg based on their bulk chemical composition. Determining the T
g of individual particles will allow for more accurate model predictions of aerosol phase state. Herein, we apply a recently developed method utilizing a nano-thermal analysis (nanoTA) module coupled to an atomic force microscope (AFM), to determine the T
g of individual secondary organic aerosol (SOA) particles generated from the reactive uptake of isoprene-derived epoxydiols (IEPOX) onto acidic ammonium sulfate aerosol particles. NanoTA works by using a specialized AFM probe which can be heated while in contact with a particle of interest. As the temperature increases, the probe deflection will first increase due to thermal expansion of the particle followed by a decrease at its melting temperature (T
m). The T
g of the particle can then be determined from Tm using the Boyer–Beaman rule. We compare the T
g of the SOA particles formed from IEPOX uptake onto ammonium sulfate particles with different initial aerosol pH values, as well as under a range of oxidant exposure conditions. Our measurements will allow for more accurate representations of the phase state of aerosols under a range of atmospheric conditions.