Secondary Organic Aerosols Derived from Intermediate Volatility n-Alkanes Adopt Low Viscous Phase State
Abstract. Secondary organic aerosol (SOA) derived from n-alkanes, as emitted from vehicles and volatile chemical products, is a dominant component of anthropogenic particulate matter, yet its chemical composition and phase state are poorly understood and hardly constrained in aerosol models. Here we provide a comprehensive analysis of n-alkane SOA by explicit chemistry modeling, machine learning, and laboratory experiments to show that, counterintuitively, n-alkane SOA adopt low viscous semisolid or liquid states. Our study underlines the complex interplay of molecular composition and SOA viscosity: n-alkane SOA with higher carbon number mostly consists of less functionalized first-generation products with lower viscosity, while the lower carbon number SOA contains more functionalized multigeneration products with higher viscosity. This study opens up a new avenue for analysis of SOA processes and the results indicate little kinetic limitations of mass accommodation in SOA formation, supporting the application of equilibrium partitioning for simulating n-alkane SOA formation in large-scale atmospheric models.
Status: open (until 29 Feb 2024)
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