Unexpected Reduction of Phenolic SOA Formation in the Presence of Electrolytic Inorganic Seed

JIWON CHOI, Myoseon Jang, University of Florida

     Abstract Number: 154
     Working Group: Aerosol Chemistry

Abstract
Phenolic hydrocarbons are abundant in biomass burning gases. They can be rapidly oxidized with atmospheric oxidants and form Secondary Organic Aerosol (SOA). In this study, The SOA formation potential from phenol and o-cresol, which are the typical phenolic hydrocarbons in biomass burning smoke, are investigated through chamber studies and the model simulation. Phenol or o-cresol is photochemically oxidized in the Atmospheric Photochemical Outdoor Reactor (UF-APHOR) under the various conditions, such as NO_x levels, humidity, temperature, and seed conditions. In our exploratory chamber study, the unexpected low SOA yield is observed for the oxidation of phenolic hydrocarbons in the presence of salted aqueous aerosol and it is even lower than no-seeded SOA. We propose that a persistent phenoxy radical heterogeneously forms in the wet inorganic aerosol and it interferes the atmospheric oxidation capability. For example, heterogeneously formed phenoxy radicals evaporate into the gas phase via gas-particle partitioning, and they fast deplete ozone. Ultimately, SOA formation can be suppressed due to the lack of the OH radical formation. The UNIPAR model that simulates SOA formation via multiphase reactions of hydrocarbons, is employed to predict the SOA formation from the photooxidation of phenol and o-cresol under varying atmospheric conditions. This model uses a volatility-reactivity base 2-D lumping array, which uses oxygenated products predicted from near explicit gas mechanisms. The UNIPAR model is capable of predicting the chamber-generated phenolic SOA mass in the absence of seed aerosol, but unsuccessful for seeded SOA due to the intervention of heterogeneously formed phenoxy radicals. The finding of this study can help to explain the low SOA yields observed during wildfires and biomass burning under the specific conditions associated with the wet inorganic aerosol.