Refining the Evolution of Gas-Particle Partitioning in Cooking Emissions Oxidation via FIGAERO-CIMS Analysis

Abstract. This study examines atmospheric oxidation and gas-particle partitioning of cooking-emitted organic aerosols. Using a Potential Aerosol Mass (PAM) flow reactor coupled with a Filter Inlet for Gases and AEROsols and a Chemical Ionization Mass Spectrometer (FIGAERO-CIMS), we monitored chemical composition, volatility distribution, and partitioning behavior under realistic conditions. A key aspect was applying high-resolution mass spectrometry within a two-dimensional volatility basis set (2-D VBS) framework to mechanistically analyze aerosol evolution. Experiments identified a two-stage particle formation: primary emissions rapidly produced fine particles (~10 nm) within two hours of oxidation, followed by secondary aerosol formation (30–50 nm) after 0.5–1 day of atmospheric aging. Oxidation products were primarily semi-volatile and intermediate-volatility organic compounds (S/IVOCs), shifting systematically toward semi-volatile organic compounds (SVOCs) over time, despite stable average molecular weight and oxidation state. Using Positive Matrix Factorization (PMF), we classified compounds by volatility and oxidation degree, identifying molecular markers for each stage. Highly oxidized small organic acids (≤C3) and C7–C10 multi-generation products were significant, showing moderate volatility and high oxidation states. A major finding was non-equilibrium gas-particle partitioning, strongly dependent on molecular class. Small organic acids and fragmentation products neared equilibrium, whereas first-generation oxidation products (C_3–8O_3–4) and large, non-fragmented compounds (>C₁₄O₅) exhibited kinetic limitations due to particle-phase diffusion constraints. This work enhances understanding of cooking aerosol behavior and provides a basis for improving emission inventories and air quality models.