Kinetic and equilibrium properties of laboratory and ambient semi-volatile organic aerosols

Organic aerosol (OA) comprises a large part of ambient aerosol and thus plays an important role in the atmospheric chemistry and climate. Understanding the properties, especially those pertaining to gas/aerosol partitioning, of this aerosol fraction is of critical importance for our ability to predict concentrations and properties of ambient aerosol. Due to the complexity of OA chemical composition, the equilibrium gas/aerosol partitioning is usually described using a simplified set of surrogate compounds, such as the Volatility Basis Set (VBS). Models are being currently developed that extend this approach by adding the second dimension on the oxygenation or polarity of compounds. However, there is practically no experimental verification that any of these approaches can accurately represent volatility behavior of complex organic mixtures. To complicate the matter, a number of recent studies have suggested that gas/aerosol equilibrium is not possible under atmospherically-relevant time scales due to kinetic limitations. In this study we investigated volatility behavior of complex laboratory-generated organic aerosol mixtures as well as of ambient aerosol sampled in Duke Forest, NC. Based on this dataset we will present an analysis of the factors influencing both kinetic and equilibrium aspects of gas/aerosol partitioning of semi-volatile organic aerosol.