Modeling Secondary Organic Aerosol Formation via Nighttime Atmospheric Chemistry of Phenolic Compounds
QUANG TRAN VUONG, Myoseon Jang, Jiwon Choi, University of Florida
Abstract Number: 161
Working Group: Aerosol Chemistry
Abstract
Increased wildfires and prescribed burnings (i.e., agricultural activities) elevate emissions of organic gases and these fire plumes degrade air quality via the formation of secondary pollutants such as ozone and secondary organic aerosol (SOA). Phenolic compounds in biomass burning smokes are known to be significant contributors to SOA production. Unlike traditional aromatic hydrocarbons, phenolic species can be oxidized during daytime and nighttime due to their high reactivity with atmospheric oxidants, such as hydroxyl radical, ozone, and nitrate radical. In this study, the SOA formation from nighttime chemistry of phenol and catechol is predicted using the UNIfied Partitioning Aerosol Reaction (UNIPAR) model, which can predict SOA mass and aerosol properties via multiphase reactions of precursor hydrocarbons. The daytime oxidation of phenol with hydroxyl radicals forms highly oxidized molecules such as multi-hydroxyphenols and multifunctional ring-opening products, which effectively yield SOA. However, phenols can form a persistent phenoxy radical (PPR), which can engage in the catalytic consumption of ozone, intervene the NOX cycle, and retard the formation of ozone and SOA. In nighttime chemistry with nitrate radicals, phenol can also form PPR along with nitro-phenols and ring-opening products. Catechol can be produced from daytime phenol oxidation (hydroxyl radical reactions), and directly emitted from biomass burning. Phenol’s reaction with ozone is negligible while catechol, which is more reactive, can react with ozone rapidly yielding ring-opening products. Through this study, product distributions of oxidized phenol or catechol are explicitly predicted for three oxidation paths (hydroxyl radical, ozone, and nitrate radical) in daytime and nighttime and applied to the UNIPAR model under varying environmental conditions (temperature, humidity, NOX levels, and inorganic seed types) to demonstrate the model performance. The suitability of gas mechanisms and SOA model is validated by simulating data obtained in a large outdoor smog reactor (UF-APHOR) chamber during daytime and nighttime.