Secondary Particulate Matter Formed in a Flow Reactor from Gas- and Aqueous-phase Chemistry of Ambient Air in Riverside, California

NINGJIN XU, Alexander B. MacDonald, Xuanlin Du, Roya Bahreini, Don Collins, University of California, Riverside

     Abstract Number: 476
     Working Group: Urban Aerosols

Abstract
Ambient particulate matter (PM) is a highly complex mixture of different-sized solid and liquid particles originating from both anthropogenic and natural sources. Secondary PM contributes a significant fraction of total PM in both urban and remote areas. However, identifying and quantifying the importance of specific precursors or precursor categories (e.g. volatile chemical products and biogenic VOCs) on measures of environmental and health-related impacts represent one of the most challenging areas of control of secondary PM. Over the last decade or so, the use of oxidation flow reactors (OFRs) to study PM formation in ambient air has grown rapidly because of their portability and their ability to provide high-time resolution measurements in dynamic environments. Use of OFRs has been almost exclusively focused on studying products and yields from gas-phase oxidation of VOCs with little or no liquid water present. Riverside, CA is located on the eastern side of the South Coast Air Basin that includes Los Angeles and often experiences high PM concentrations. In the spring of 2022, the first of a series of field studies aimed at understanding the sources of PM in different regions of California was conducted in Riverside. The Aerosol Production and Processing of Aerosols (APPA) OFR was operated continuously for one month to measure the amount and properties of secondary PM formed through both gas- and gas+aqueous-phase oxidation. The results are used to characterize short-term variability in PM precursors and to explore the roles of different formation pathways. The secondary PM formed in the OFR was measured with a scanning mobility particle sizer and a mini time-of-flight aerosol mass spectrometer (mAMS). We will provide an overview of the experimental approach and will present initial results from the field study.