Optical growth of highly viscous organic/sulfate particles

Light extinction by atmospheric particles is strongly dependent on their chemical composition and water content. Since light extinction directly impacts climate, optical measurements of atmospherically relevant aerosols at varying relative humidities (RH) are needed. Recent studies have highlighted the possibility that some atmospheric aerosols are glassy under ambient conditions. Here, the particle optical growth factor, fRH_ext, was measured for liquid and glassy particles using cavity ring-down aerosol extinction spectroscopy. The particles were composed of ammonium sulfate (AS), 1,2,6-hexanetriol, sucrose, raffinose, and mixed particles containing AS and either sucrose or raffinose. Both sucrose and raffinose can be glassy at room temperature. For the pure organics, the highly viscous sucrose and raffinose particles have similar optical growth curves to the liquid 1,2,6 hexanetriol particles. However, for particles composed of sucrose or raffinose mixed with AS, optical growth depends on the AS weight-percent, which in turn controls the phase state of the AS and ultimately the water uptake.