Use of an Oxidation Flow Reactor in the Field to Study Ambient Secondary Aerosol Formation from Gas- and Aqueous-Phase Chemistry
YING ZHOU, Alexander B. MacDonald, Ningjin Xu, Xuanlin Du, Roya Bahreini, Don Collins,
University of California, Riverside Abstract Number: 477
Working Group: Urban Aerosols
AbstractAn oxidation flow reactor (OFR) was employed to study the gas- and aqueous-phase chemistry that leads to secondary aerosol (SA) formation in ambient air. The Accelerated Production and Processing of Aerosols (APPA) reactor with a Perfluoroalkoxy Alkane (PFA) Teflon flow tube has been redesigned to achieve portability for field experiments. The project aims to develop an effective approach to mitigate emissions from different sources sufficiently to meet federal standards for the two major criteria air pollutants: O
3 and PM
2.5. The project involves 4-week field studies at sites in Riverside, CA (October 2022), Wilmington, CA (March 2023), and Bakersfield, CA (planned for winter, 2024). Riverside represents the Inland Empire region of southern California where prevailing westerly winds frequently bring high PM and is also notably influenced by emissions from the goods movement industry, while Wilmington and Bakersfield are significantly impacted by port and truck emissions, and energy and agricultural production, respectively. A Scanning Mobility Particle Sizer (SMPS) and a compact time of flight mini Aerosol Mass Spectrometer (mAMS) are used to sample the processed air exiting the APPA reactor. To investigate the effect of OH exposure and liquid water content on SA formation, OH exposure over the average reactor residence time of ~150 s was varied from ~1 × 10
11 to ~5 × 10
11 molec cm
-3 s by changing the externally added O
3 concentration, while relative humidity (RH) inside the APPA reactor was cycled between 40%, 85% and 100%, for which dry seed aerosol, aqueous seed aerosol and cloud droplets were present in the reactor, respectively. Organic aerosol (OA) concentration generally increased with OH exposure and with aerosol/droplet water content. In addition, OA concentration was higher at nighttime than during the day, presumably because of accumulation of reactive precursors in the absence of ambient photochemistry.