Chlorine-initiated oxidation of alkanes under high-NO conditions: Insights into secondary organic aerosol composition and volatility using a FIGAERO-CIMS

Abstract

Chlorine-initiated oxidation of alkanes (C8g'12) under high-nitrogen oxide conditions was investigated. Observed secondary organic aerosol yields (0.16 to 1.65) are higher than those for OH-initiated oxidation of C8ĝ12 alkanes (0.04 to 0.35). A high-resolution time-of-flight chemical ionization mass spectrometer coupled to a Filter Inlet for Gases and AEROsols (FIGAERO-CIMS) was used to characterize the gas- and particle-phase molecular composition. Chlorinated organics were observed, which likely originated from chlorine addition to the double bond present on the heterogeneously produced dihydrofurans. A two-dimensional thermogram representation was developed to visualize the composition and relative volatility of organic aerosol components using unit-mass resolution data. Evidence of oligomer formation and thermal decomposition was observed. Aerosol yield and oligomer formation were suppressed under humid conditions (35 % to 67 % RH) relative to dry conditions (under 5 % RH). The temperature at peak desorption signal, max, a proxy for aerosol volatility, was shown to change with aerosol filter loading, which should be constrained when evaluating aerosol volatilities using the FIGAERO-CIMS. Results suggest that long-chain anthropogenic alkanes could contribute significantly to ambient aerosol loading over their atmospheric lifetime.