Relationships of the Hygroscopicity of HULIS With Their Degrees of Oxygenation and Sources in the Urban Atmosphere

Humic-like substances (HULIS) are unresolved compounds isolated from organic matter in atmospheric aerosols. Understanding the chemical structures and sources that control the hygroscopicity of HULIS is important for predicting its environmental impacts and possibly useful for parameterization of the hygroscopicity of organic aerosol (OA). Here, the hygroscopic growth of HULIS from total suspended particles samples in Beijing was analyzed using a hygroscopicity tandem differential mobility analyzer. The hygroscopicity parameter of HULIS (kappa(HULIS)) was determined to be 0.06 & PLUSMN; 0.03, and was found to correlate positively with O:C and f(44) from offline aerosol mass spectrometry. Additionally, kappa(HULIS) was correlated positively with oxygenated organic aerosol (OOA) and correlated negatively with cooking OA and biomass burning OA, for which the source-related OA types were from mass-spectral-based positive matrix factorization analyses. Further analysis resolved substantial kappa values of 0.09 and 0.22, respectively, for less-oxidized and more-oxidized OOA, in contrast to the low kappa values for cooking OA and biomass burning OA. Extensions of O:C- and source-based parameterizations reasonably estimated the hygroscopicity of total OA with a moderate contribution from HULIS. This result and the fact that the obtained OOA contributions to kappa of OA were similar to those from different environments suggest the applicability of parameterizing the hygroscopicity for a wide range of OA in particular based on source-related structural characteristics.