To better understand the effect of SOM particles on the Earth's climate, several characteristics of SOM particles of different compositions have been studied. Diffusion rates are essential for the investigation of processes such as particle growth and the rate of heterogeneous reactions within SOM particles. In the past, diffusion rates of SOM particles have been estimated by converting viscosity values into diffusion coefficients using the Stokes-Einstein relation.
Here, we present values of diffusion coefficients, which were measured directly using the fluorescence microscopy method FRAP (fluorescence recovery after photobleaching), of organic dyes in organic-water proxies of atmospheric particles. Fluorescent dyes of varying sizes and molecular weights (320-1.50x105 g/mol) were used and diffusion coefficients were measured across a wide range of relative humidities (40-93% RH). These measurements add to the limited amount of data on the diffusion rate constants of organics within organic-water solutions.