AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Predicting the Phase State of Secondary Organic Aerosol and Understanding its Influences on the Heterogeneous Ice Nucleation
YUE ZHANG, Martin Wolf, Shachi Katira, Jason Injae Jung, Abigail Koss, Peyton Spencer, Xiaoli Shen, Andrew Lee, Andrew Lambe, Wen Xu, Leonid Nichman, Yuzhi Chen, Manjula Canagaratna, Zhenfa Zhang, Avram Gold, John Jayne, Douglas Worsnop, Paul Davidovits, David Chandler, Timothy Onasch, Charles Kolb, Jesse Kroll, Jason Surratt, Daniel Cziczo, Univ. of North Carolina, Chapel Hill/Aerodyne Research, Inc.
Abstract Number: 911 Working Group: Aerosols, Clouds and Climate
Abstract Particulate matter (PM) has important effects on the climate, human health, and visibility. Recent studies have shown that some organic particles can transform from a liquid/semi-solid phase state to a glassy phase state as temperature, humidity, and composition change. Glass transitions have important implications for reactivity, growth, and cloud formation capabilities of organic aerosols (OA), and is also an important constraint for estimating aerosol viscosity.
The glass transition temperatures (Tg) of selected organic components and organic-organic binary mixtures were measured at selected atmospherically relevant cooling rates (2-10 K/min). The results indicate that increasing the cooling rate can reduce the glass transition temperatures of organic compounds by 4-5 K, leading aerosol becoming glassy 400-800 meter lower in the ambient atmosphere than the base condition. A semi-empirical relationship between the glass transition temperatures and aerosol volatility is also established through experimental measurements and modeling, facilitating parameterization of aerosol viscosity and phase state into regional and global models.
Given that in the free troposphere OAs can exist in semi-solid or solid phase states, such transition of the phase state may potentially increase the heterogeneous IN activity. A laboratory study was systematically performed to examine the effects of aerosol-phase state on heterogeneous IN properties of OAs by using the spectrometer for ice nucleation (SPIN), a commercially available instrument (Droplet Measurement Technologies, Inc), potential aerosol mass (PAM) oxidation flow reactor, and the MIT environmental chamber.
OAs comprised of representative surrogates and the actual secondary organic aerosols (SOA) from various precursors were generated and passed through a temperature control apparatus, where the temperature of the aerosols was kept between -45~20°C before entering the SPIN. Our results show that certain pre-cooling the aerosol particles enhances the IN onset relative humidity (RH) and the active fraction of IN. Coupled with viscosity and glass transition temperature calculations, the aerosol phase state changes is shown to be the reason for the enhanced ice nucleation, however the chemical composition of the aerosols also have important influences on the IN properties.