Exploring the Mechanisms of New Particle Formation in Houston with an Outdoor Chamber
JEREMY WAKEEN, Xuanlin Du, Samuel O'Donnell, Don Collins, Jeffrey R. Pierce, James Smith, University of California, Irvine
Abstract Number: 382
Working Group: Urban Aerosols
Abstract
New particle formation (NPF) has been shown to occur in urban areas with high pre-existing particle concentrations, but the mechanisms of nucleation and growth are poorly understood. NPF events have been observed previously in Houston, TX, however no direct measurements of the composition of newly formed particles or gaseous precursors have been performed. During July and August 2022, the TRacking Aerosol Convection interactions ExpeRiment (TRACER) in Houston, we deployed a suite of instruments to measure highly oxidized molecules (HOMs) and 10-100 nm diameter nanoparticles formed in the Captive Aerosol and Growth Evolution (CAGE) chamber that removes ambient pre-existing particles so that only ambient gases undergo photooxidation and gas-particle conversion. Particles formed in CAGE can be compared to those in ambient air, providing insights into the importance of local and regional emission sources and transport processes. We measured nanoparticle composition formed in CAGE using Thermal Desorption Chemical Ionization Mass Spectrometry (TDCIMS) and gas-phase HOMs using nitrate-CIMS. Measurements are supplemented by process-level modeling of gas-phase oxidation chemistry, including HOM formation and aerosol microphysics such as nucleation, coagulation, condensation, and evaporation. NPF was observed nearly every day, sometimes multiple times in a day, in CAGE during the observation period. TDCIMS measurements indicate sulfate, multifunctional organosulfates, amines, ammonium, and other highly functionalized organics dominate the composition of these newly formed particles. The model successfully reproduces the timing of these events and predicts an important role for both sulfuric acid as well as oxidation products of aromatics in these events.