Collaborative Research – BC5 laboratory studies of the optical properties and ice nuclei activity of carbonaceous particles as a function of mixing state and phase state

Description

We are developing new techniques for studying the formation, chemical composition, phase state, and cloud activity, including cloud condensation nuclei (CCN) and ice nuclei (IN), of atmospherically relevant particles. (1) In collaboration with Dr. Cziczo (MIT), we are systematically studying the ice nucleation of black carbon containing particles. Our recent work has tested the IN activity of various kinds of black carbon particles before and after they undergo oxidation and organic coating. Our objective is to study changes in the surface properties and morphologies of black carbon particles to investigate the dominant factors that define IN activity. Modeling of ice and mix phase cloud formation based on current emission data and atmospheric processes are not well quantified. (2) We are combining our new method of measuring SOA glass transitions with IN activity to study the effects of organic particle phase states on IN activities, in collaboration with Drs. Cziczo from MIT and Knopf from Stony Brook University. Recent work by our research group and others investigating ice nucleation of glassy organic aerosols suggest that the phase state of SOA particles from biogenic sources may influence ice (e.g., cirrus) and mixed phase cloud formation. Given that a significant fraction of global particles are composed of SOA material, which may become glassy and exhibit efficient ice nucleation in the free troposphere, SOA may contribute significantly to the global IN budget. (3) We are preparing for our final Boston College – Aerodyne Black Carbon study in May, 2018. Our objective is to generate laboratory distributions of nascent, thinly coated, and thickly coated soot particles to tease out the varying effects of intra-particle (i.e., morphology) and inter-particle (i.e., population) mixing states on observed absorption enhancement effects. Recent laboratory and field work, including the studies of our research group, have documented a wide variation in the measured absorption enhancements of internally mixed soot particles, from near zero in California to greater than a factor of 2 in the laboratory. Uncertainties regarding the reasons of this variation has a direct impact on atmospheric models and our ability to estimate the impacts of particle loading and to predict future climate.