Measurement of Secondary Aerosol Formation in Ambient Urban Air Using Dual Portable Outdoor Chambers
XUANLIN DU, Alexander B. MacDonald, Ningjin Xu, Ying Zhou, Roya Bahreini, Don Collins,
University of California, Riverside Abstract Number: 581
Working Group: Urban Aerosols
AbstractFine particulate matter (PM) causes serious effects on human health, air quality, and climate. Secondary aerosol (SA) is a major component of fine PM and is formed through chemical reactions involving precursor gases such as sulfur dioxide, nitrogen oxides, ammonia, and volatile organic compounds (VOCs). However, the formation, sources, and sensitivity of SA to different gas precursors need to be better understood. Most studies on the formation and properties of SA use traditional Teflon chambers in which one or more precursors are injected and UV lights are employed.
In this study, we present observations made using a complementary approach, for which a pair of 2-cubic meter portable chambers were operated with entirely or mostly ambient air under natural light conditions. We operated the Captive Aerosol Growth and Evolution (CAGE) chambers during three field studies, with the first two during spring and early fall 2022 in Riverside, CA, and the third during late winter 2023 in Wilmington, CA. We utilized two identical CAGE chambers to measure the sensitivity of SA concentration and composition to addition of different precursor gases. Monodisperse seed particles were injected intermittently into both chambers. We added a fixed concentration of NO2, VOCs, or NH3 into one of the chambers, while the other served as a reference chamber in which the gas composition mirrored ambient air just outside. The composition and volume concentration of the secondary aerosol formed in the chambers were quantified using an aerosol mass spectrometer (AMS) and a scanning mobility particle sizer (SMPS), respectively. We observed mass concentration enhancements and more frequent nucleation and growth of particles in the perturbation chamber after introducing VOCs and NH3 relative to the reference chamber. Together with simultaneously measured trace gas concentrations, the measurements of secondary aerosol in the chambers were used to investigate the responsible species and mechanisms.