Secondary Organic Aerosol from Gas- and Aqueous-phase Oxidation of Volatile Organic Compounds in an Oxidation Flow Reactor
NINGJIN XU, Chen Le, Kunpeng Chen, Ying-Hsuan Lin, David R. Cocker III, Don Collins,
University of California, Riverside Abstract Number: 479
Working Group: Aerosol Chemistry
AbstractA large fraction of organic aerosol (OA) in the atmosphere is secondary (SOA), produced either through the photooxidation of volatile organic compounds (VOCs) from biogenic and anthropogenic sources (gasSOA), or by irreversible aqueous phase reactions of organic compounds via cloud/fog droplets or wet aerosols (aqSOA). SOA formation through aqueous phase reactions could be significant, with several reaction pathways and products identified and studied. However, the production of aqSOA is hard to quantify and the importance of different mechanisms is still poorly understood, which is partly due to the lack of available measurement tools and techniques. Whereas quantification of the SOA yield resulting from gas phase oxidation of VOCs is fairly straightforward, determining the impact of further reaction of the products in liquid water is more challenging. Few studies have explored the contribution of different VOCs via aqueous phase chemistry relative to that via gas-phase pathways.
Here, we present experimental results of SOA formation through gas- and aqueous-phase oxidation of a variety of VOCs using a newly developed multiphase oxidation flow reactor, the Accelerated Production and Processing of Aerosols (APPA) reactor. Experiments were performed by oxidizing the VOCs in the presence of dry, aqueous, or activated seed particles inside the OFR, where the relative humidity (RH) was maintained between 40 and 100%. We report the SOA yield for gas- and gas+aqueous-phase oxidation as a function of OH exposure (OHexp). The properties of the aerosol-phase products were characterized by a high-resolution time-of-flight aerosol mass spectrometer (AMS) and a chemical ionization time-of-flight mass spectrometer (CIMS). We also report the SOA yield as a function of liquid water content, seed aerosol type, and dry seed aerosol surface area.