Chemical Composition and Volatility of Phenol Photooxidation Products in the Presence of NOx
DAVID PANDO, Michelia Dam, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 358
Working Group: Combustion
Abstract
Phenol is emitted into the atmosphere by anthropogenic and biogenic thermal processes such as wildfires, prescribed fires, and combustion engines. It is efficiently oxidized by hydroxyl (OH) radical, forming gas products with increased functionality and secondary organic aerosols (SOA) after aging in the atmosphere. Phenol is often co-emitted with high concentrations of NOx (sometimes up to ppm levels), which can react with the oxidized products to form nitroaromatics or organonitrates. These products can have different light absorbing properties and vapor pressures than non-nitrogen containing products, therefore impacting radiative climate effects and SOA formation. In this study, we measure chemical composition and estimate vapor pressure of gas and particle products of this system.
Phenol photooxidation was simulated in the Georgia Tech Environmental Chamber facility. A series of instruments is connected to the chamber to measure gas and particles: FIGAERO-CIMS, SMPS, GC-FID, and NOx monitor. Our results show that nitrogen containing organic compounds (including nitroaromatics) with 6-carbon atoms make up 40-80% of total organic particle signal from FIGAERO measurements, with nitrocatechol, nitrophenol, and C6H5NO5 as the dominant species. Increasing phenol:OH ratio and initial seed aerosol surface area increase the fraction of these compounds partitioning to the particle phase. At lower phenol:OH chemical regimes, the fraction of non-nitrogen containing oxygenated fragmentation products (C2-C5) in the gas and particle phase increases, likely owing to enhanced multigenerational chemistry facilitated by longer lived early generation products (lower condensation sink) and a higher excess of oxidant. Increasing the initial seed aerosol surface area results in the volatility of CHO species increasing in the gas phase and decreasing in the particle phase. The volatility of CHON species in the gas phase does not change with increasing initial seed aerosol surface area, however, in the particle phase, it increases as the initial seed aerosol surface area increases.