PNNL

Abstract

Quantitative assessment of gas-particle partitioning of individual components within complex atmospheric organic aerosols (OA) mixtures is critical for predicting and comprehending the formation and evolution of OA particles in the atmosphere. This investigation leverages previously documented data obtained through a temperature programmed desorption - direct analysis in real time – high resolution mass spectrometry (TPD-DART-HRMS) platform. This methodology facilitates the bottom-up construction of volatility basis set (VBS) distributions for constituents found in three biogenic secondary organic aerosol (SOA) mixtures produced through the ozonolysis of a-pinene, limonene, and ocimene. The apparent enthalpies (?H*sub) and saturated vapor mass concentrations (C*T, µg?m-3) of individual SOA components, determined as a function of temperature (T, K), facilitated an assessment of changes in VBS distributions and gas-particle partitioning with respect to T and atmospheric total organic mass loadings (tOM, µg?m-3). The VBS distributions reveal distinct differences in volatilities among monomers, dimers, and trimers, enabling their categorization into separate volatility bins. At the ambient temperature of T = 298 K, only monomers efficiently partition between gas and particle phases across a broad range of atmospherically relevant total organic mass loadings (tOM)values of 1–100 µg?m-3. Partitioning of monomers and trimers becomes notable only at T >360 K and T >420 K, respectively. The viscoelastic properties of SOA mixtures are assessed using a bottom-up calculation approach, incorporating input values such as the SOA components’ elemental formulas, ?H*sub, C*T, and particle-phase mass fraction values. Through this approach, we are able to accurately estimate the variations in SOA viscosity that result from the evaporation of its components, which, in turn, are influenced by atmospherically relevant changes in tOM and T. Comparison of the calculated SOA viscosity and diffusivity values with literature reported experimental results shows close agreement, thereby validating the employed calculation approach. These findings underscore the significant potential for TPD-DART-HRMS measurements to facilitate untargeted analysis of organic molecules within OA mixtures, enabling a quantitative assessment of their gas-particle partitioning and the estimation of their viscoelastic properties and contributing valuable insights to atmospheric models.