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Volatility and Viscosity Are Correlated in Terpene Secondary Organic Aerosol Formed in a Flow Reactor

Secondary organic aerosol (SOA) is a complex mixture of largely unspeciated compounds. The volatility and viscosity of the bulk organic aerosol influence new particle formation, processing, and lifetime in the atmosphere. Relationships between these properties are well-defined for pure compounds but currently unavailable for bulk organic aerosol. In this survey study, we characterized SOA formed from a range of biogenic precursors and conditions in an oxidation flow reactor for volatility (thermodenuder), viscosity (dimer coagulation, isolation, and coalescence), and oxidation state (aerosol chemical speciation monitor). We find linear trends in log–linear and log–log plots of single-parameter representations of volatility and viscosity, with higher condensed-phase fractions of extremely low and low volatility material associated with an increased viscosity (R = 0.69). Per this relationship, an increase in the contribution of these fractions (i.e., lower volatility) by 0.1 results in an increase in viscos...