where A and B are coefficients with values of 0.73 and 1.79, respectively. rdiff and rmatrix are the hydrodynamic radii of the diffusing molecules and matrix molecules, respectively. For CO2, we used a rdiff of 0.103 nm. For rmatrix, we used a value of 0.406 nm, based on the weighted average of the molecular weights shown in Table , an assumed spherical geometry of the matrix molecules, and a density of 1.4 g L -1 for catechol SOA. A rmatrix of 0.406 nm yielded ξ = 0.54.