Secondary Organic Aerosol Formation from Gasoline Vehicle Exhaust Investigated in a Dual Outdoor Chamber System

XUANLIN DU, Jinsheng Zhang, Linhui Tian, Ying-Hsuan Lin, Don Collins, University of California, Riverside

     Abstract Number: 588
     Working Group: Carbonaceous Aerosol

Abstract
Organic aerosol (OA) is a primary contributor to atmospheric fine particles, which cause serious effects on human health, air quality, and climate. Secondary organic aerosol (SOA) contributes the largest fraction of OA in urban areas and is formed from the oxidation of organic vapors. Vehicle emissions are a significant source of SOA precursors. However, the formation mechanisms and chemical composition of SOA from vehicle emissions remain to be fully understood. Furthermore, most studies of SOA from vehicle emissions have utilized a traditional batch chamber in which UV lights are used or an oxidation flow reactor, introducing potential bias due to high oxidant concentrations.

In this study, we employed a complementary approach using a pair of 2-cubic meter outdoor Captive Aerosol Growth and Evolution (CAGE) chambers. The CAGE chambers are operated with entirely or mostly ambient air under natural light conditions, which is more representative of the conditions under which SOA will form in the atmosphere than with indoor UV photo simulations. Idling gasoline vehicle exhaust diluted into ambient air was introduced into one of the chambers (called the perturbation chamber), while the other served as a reference chamber in which the gas composition mirrored ambient air just outside. Significant nucleation and growth of particles were observed in the perturbation chamber, suggesting the important role of vehicle exhaust in new particle formation in the atmosphere. To further understand SOA formation under real-world atmospheric oxidation, the molecular-level composition of secondary aerosol collected on filters was analyzed using a chemical ionization time-of-flight mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS). The results present a series of special organic particle-phase species formed from vehicle exhaust, which will benefit SOA source apportionment efforts.