Accurate Prediction of Organic Aerosol Evaporation Using Kinetic Multilayer Modeling and the Stokes–Einstein Equation

Abstract

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.

A Kinetic Model for Predicting Trace Gas Uptake and Reaction

“…Smith et al examined the uptake and reaction of O 3 with oleic acid, comparing the resistor model with results obtained by numerically solving the coupled partial differential equations for diffusion and reaction. Kinetic multilayer models − employ a flux-based representation, numerically solving the coupled differential equations for mass transport and chemical reactions. Many multilayer models require a comprehensive set of variables for each molecule and so are often employed in inverse modeling studies , of large data sets, where they can resolve the fine details of surface and bulk processes as well as the formation of chemical gradients.…”

Fluorescence Recovery after Photobleaching in Colloidal Science: Introduction and Application

“…Colloids are particles that are submicrometric, and they undergo random Brownian diffusion. Robert Brown quantitatively depicted diffusive motion as a mean-squared displacement (dependent on medium temperature) that was inversely linked to the object’s hydrodynamic radius and medium viscosity (i.e., the Stokes–Einstein relationship) . In other words, if one observes microstructural changes in a medium, based on random thermal movement, these movements along with their associated movement can be studied with confocal microscopy.…”

A Kinetic Model for Predicting Trace Gas Uptake and Reaction

“…Smith et al 22 examined the uptake and reaction of O3 with oleic acid, comparing the resistor model with results obtained by numerically solving the coupled partial differential equations for diffusion and reaction. Kinetic multilayer models [31][32][33][34][35][36][37][38] employ a flux-based representation, numerically solving the coupled differential equations for mass transport and chemical reactions. Many multilayer models require a comprehensive set of variables for each molecule and so are often employed in inverse modeling studies 5,39 of large data sets, where they can resolve the fine details of surface and bulk processes as well as the formation of chemical gradients.…”