Effects of RH and UV Light on the Formation, Composition, and Aging of SOA Derived from the High-NOx Oxidation of Ethylbenzene by Chlorine Radical

LEIF JAHN, Lea Hildebrandt Ruiz, University of Texas at Austin

     Abstract Number: 381
     Working Group: Aerosol Chemistry

Abstract
Akylaromatic molecules are a class of volatile organic compounds (VOCs) that comprise a substantial source of secondary organic aerosol (SOA) precursors in urban and other polluted environments. Despite the importance of SOA derived from alkylaromatic VOCs, unknowns remain regarding how SOA forms and transforms in response to environmental factors such as relative humidity (RH) and ambient UV light. In the present work, we generate alkylaromatic SOA during laboratory chamber experiments and examine how SOA composition changes under different RH and lighting conditions. We choose to examine SOA formed during the reaction of ethylbenzene and chlorine radical under high-NOx conditions, typical of urban environments where alkylaromatic VOCs are common. The usage of chlorine radical enables the targeted study of alkylaromatic molecules and SOA formed when oxidation is initiated along the alkyl chain, a more minor pathway for OH chemistry compared to ring addition that becomes more prominent in larger alkylaromatic molecules. Gas-phase measurements using chemical ionization mass spectrometry (CIMS) show oxidation products consistent with initial oxidation along the ethyl chain followed by subsequent multigeneration reactions with OH radical formed through secondary chemistry. A Filter Inlet for Gases and Aerosols (FIGAERO) attachment for an I- CIMS and an aerosol chemical speciation monitor (ACSM) were used to analyze and compare aerosol composition across different RH and lighting conditions and over different timescales.