Organic aerosol can adopt a wide range of viscosities, from liquid to glass, depending on the local humidity. In highly viscous droplets, the evaporation rates of organic components are suppressed to varying degrees, yet water evaporation remains fast. Here, we examine the coevaporation of semivolatile organic compounds (SVOCs), along with their solvating water, from aerosol particles levitated in a humidity-controlled environment. To better replicate the composition of secondary aerosol, nonvolatile organics were also present, creating a three-component diffusion problem. Kinetic modeling reproduced the evaporation accurately when the SVOCs were assumed to obey the Stokes-Einstein relation, and water was not. Crucially, our methodology uses previously collected data to constrain the time-dependent viscosity, as well as water diffusion coefficients, allowing it to be predictive rather than postdictive. Throughout the study, evaporation rates were found to decrease as SVOCs deplete from the particle, suggesting path function type behavior.
Bibliographical noteFunding Information:
S.I. acknowledges funding from GW4+ DTP from NERC(NE/L002434/1). C.S.D. acknowledges funding from the U.S. National Science Foundation (CAREER, AGS-1554936). M.S. acknowledges funding from the U.S. National Science Foundation (CAREER, AGS-1654104). The authors are grateful to Thomas C. Preston for the sharing of software used in radius fitting, described in the supplement.
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