Abstract

Organic aerosol particles play major roles in atmospheric chemistry, climate, and public health. Aerosol particle viscosity is important since it can determine the ability of chemical species such as oxidants, organics or water to diffuse into the particle bulk. Recent measurements indicate that OA may be present in highly viscous states, however, diffusion rates of small molecules such as water appear not to be limited by these high viscosities. In collaboration with Markus Kalberer (University of Cambridge) and Marina Kuimova (Imperial College London) a new technique for measuring viscosity has been developed that allows for the imaging of aerosol viscosity in micron sized aerosols through use of fluorescence lifetime imaging of viscosity sensitive dyes. This work has been conducted both on aerosols deposited on microscope coverslips and on particles that are levitated in their true aerosol phase through the use of a bespoke optical trap developed at the Central Laser Facility at the Rutherford Lab in Oxford. The technique allows for the direct observation of kinetic barriers caused by high viscosity and low diffusivity in aerosol particles. It can dynamically quantify and track viscosity changes during atmospherically relevant processes such oxidation and hygroscopic growth. A range of aerosol systems have been studied, and will be discused, including secondary organic aerosol (SOA) and bioaerosols includuing pollen and fungal spores.