I am an atmospheric chemist interested in suspended particles, or aerosols, focusing on particulate organic matter. My Ph.D. investigated the influence of organic matter on aerosol cloud condensation nuclei (CCN) activity. Because all cloud droplets in the atmosphere form on pre-existing particles, aerosols can influence climate indirectly via changes in cloud properties. I found that in some settings, CCN activity was reduced due to a slower droplet growth rate, likely due to an organic film covering the droplet surface. I also developed a technique allowing size of droplets formed on lab-generated particles to be measured at high RH (99.1 - 99.9%), higher than most other such measurements. Measurements at high RH, in addition to being rare, are also especially important because they occur at similar water activities and surface:volume ratios as typical atmospheric CCN, and are uniquely sensitive to the surface activity of organic matter.
More recently, I have begun investigations into the chemistry of submicron particles and droplets with collaborators at LBL, UC Berkeley, and elsewhere. We investigate the products formed during heterogeneous oxidation of model hydrocarbons, and use the Chemical Dynamics Beamline (9.0.2) as a "soft" ionization source allowing the positional isomers of first-generation alcohols and carbonyls to be distinguished. These isomer distributions suggest that alkoxy radicals are a key intermediate in this reaction, and for some compounds indicate the orientation of molecules at the particle surface (which may be different than the bulk particle). We are also attempting to make similar measurements of heterogeneous chemistry but at high RH, such that droplets have formed on all particles. This will allow questions about the cloud (aqueous-phase) processing of organic aerosol to be tested.