Measurement of Secondary Aerosol Formation in Ambient Air using Portable Outdoor Chambers

XUANLIN DU, Alexander B. MacDonald, Ningjin Xu, Roya Bahreini, Don Collins, University of California, Riverside

     Abstract Number: 550
     Working Group: Urban Aerosols

Abstract
Secondary aerosol has impacts on health, air quality, and climate. It is formed through various gas-to-particle processes and can be produced from gases emitted from biogenic, anthropogenic, and biomass burning sources upon atmospheric oxidation. The formation, sources, and sensitivity to changing gas precursors need to be better understood. Most studies of the formation and properties of secondary aerosol use traditional Teflon environmental chambers in which one or more precursors are injected and oxidized and the resulting aerosol is measured. Here, we summarize observations made using a complementary approach, for which a pair of 2-cubic meter portable chambers are operated with entirely or mostly ambient air at the location of interest. The Captive Aerosol Growth and Evolution (CAGE) chambers were used during a pair of field studies in Riverside, CA, with the first in spring, 2022, and the second in late summer/early fall, 2022. The two identical CAGE chambers were utilized to measure the sensitivity of secondary aerosol concentration and composition to changing precursor gas concentrations by operating one chamber as a reference chamber in which the gas composition mirrored that of ambient air just outside and the second as a perturbation chamber through the controlled addition of a fixed concentration of NOx, VOCs, or NH3. Monodisperse seed particles were intermittently injected into both chambers and the composition and volume concentration of the secondary aerosol formed on them were quantified using mini aerosol mass spectrometer (mAMS) and a scanning mobility particle sizer (SMPS), respectively. Together with simultaneously measured trace gas concentrations, the measurement of secondary aerosol in the chambers is used to investigate the responsible species and mechanisms.