A Pseudo-Lagrangian Perspective on New Particle Formation and Growth Observed in Urban Outflow Plumes during AEROMMA
EN LI, Charles Brock, Andrew Rollins, The AEROMMA Team, Shantanu Jathar, Jeffrey R. Pierce, Colorado State University
Abstract Number: 218
Working Group: Coast to Coast Campaigns on Aerosols, Clouds, Chemistry, and Air Quality
Abstract
New particle formation (NPF) events, especially in urban settings, have mostly been observed from ground sites and offer limited information on the evolution of aerosol size distribution within the NPF plume. Traditional NPF precursor gases such as H2SO4 (from SO2 oxidation) and mobile sources of volatile organic compounds (VOCs), as well as an non-traditional class of volatile chemical product (VCP) VOCs play an important role in urban air pollution and contribute to secondary organic aerosol (SOA) formation, either through NPF and increase the particle number concentration or through growth by condensation and increase the particle mass concentration. As part of the synergistic effort by AGES+ to understand the emerging role of VCPs in urban air quality, the Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) campaign made a suite of gas- and particle-phase measurements over US megacities and Toronto. Using the AEROMMA dataset, we focus on cases of pseudo-Lagrangian sampling and investigate the contribution of traditional and non-traditional NPF precursor gases to the particle size distribution in urban outflow. In our preliminary results, we identify an urban NPF event on August 1, 2023 around Chicago with the median particle diameter growing from ~7 nm in the source region to ~25, ~50, ~90 nm approximately 30, 90, and 160 km downwind, respectively. Back-trajectory calculations, in addition to Laser Induced Fluorescence (LIF) SO2 measurements and VOC measurements from the PTR-ToF-MS and LToF-CIMS mass spectrometry instruments, suggest nucleation is initiated in SO2-rich industrial outflow from Gary, IN; and subsequent growth is promoted in VCP-rich urban outflow from Chicago, IL. Complementary work uses the Statistical Oxidation Model coupled with the TwO Moment Aerosol Sectional (SOM-TOMAS) aerosol microphysics model to evaluate the individual contribution of various traditional and non-traditional semivolatile precursor gases to NPF and subsequent growth.