Glass transitions from a liquid or semi-solid to solid phase state have important implications for the multiphase and interfacial chemistry of secondary organic aerosols (SOAs) in the atmosphere. Glass transitions change the reactive uptake coefficient and gas phase diffusivities of these particles, affecting their particle phase reactivity, growth, and cloud forming capabilities. The small size of SOA particles makes it challenging to measure glass transition parameters using conventional methods. This study examined the glass forming properties of various SOA surrogates and their tracers by measuring the dielectric behavior of their thin films on interdigitated electrodes (IDEs). Organic aerosol particles were deposited onto IDE substrates using electrostatic precipitation and were observed to form uniform thin films. The thin films were then analyzed by dielectric spectroscopy, which probes dipole relaxation dynamics of organic samples as a function of temperature and relative humidity. This information was used to calculate the glass transition temperatures of single compound, simple mixture SOA surrogates and tracers. Dielectric spectra were obtained as a function of the cooling rate. The results indicate that vary the cooling rates can induce a 3-6 K difference in the glass transition temperature for SOA surrogates and tracers (as shown in Figure 1). The temperature difference corresponds to about 1 km height in the ambient atmosphere for the corresponding updraft velocities. Our results underscore the general lack of information on the spatial and temporal changes in SOA particle phase that may have significant effects on multiphase reactivity and cloud formation in the atmosphere.

Glass forming properties of secondary organic aerosol tracers and surrogates examined by thin film dielectric relaxation spectroscopy

254th National Meeting (2017)

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