AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Rethinking Secondary Organic Aerosol Formation from Aromatic Hydrocarbons: Role of NOx, ·OH and Substitute
LIJIE LI, Ping Tang, Chia-Li Chen, Shunsuke Nakao, Li Qi, David R. Cocker III, University of California, Riverside
Abstract Number: 276 Working Group: Aerosol Chemistry
Abstract Aromatic hydrocarbons account for 20%-30% of the VOC in the urban atmosphere and are major contributors to anthropogenic SOA. Yet, prediction of SOA from aromatic hydrocarbons as a function of structure, NO$_x and OH radical level remains elusive. This study generalizes the relationship between aromatic alkyl groups (number and location on aromatic ring) and SOA formation from aromatic hydrocarbon under both low NO$_x and H$_2O$_2 only conditions based on hundreds of chamber experiments from 18 different aromatic precursors. First, the relationship of SOA yields with the number of alkyl group is quantified and presented in a novel manner. Second, the concept of low and high yield of aromatics is revisited and modified accordingly. Third, SOA chemical compositions among these aromatics are unified by analyzing elemental ratio measured by ToF-HR-AMS. Finally, $^(13)C isotope enriched aromatics are used to confirm the contribution of alkyl group to SOA formation. Three mass spectrometers including ToF-HR-AMS, PTR-MS (Proton Transfer Reaction – Mass Spectrometry) and SIFT (Selected-ion flow-tube mass spectrometry) are used to study alkyl group impacts on SOA formation and composition during photooxidation. Finally, a general mechanism of SOA formation from aromatic hydrocarbon is proposed.