In-Situ Secondary Organic Aerosol Formation Rate in Houston during the Tracking Aerosol Convection Interactions Experiment (Tracer) Field Campaign
CHUN-YING CHAO, Fangzhou Guo, Donna Sueper, Subin Yoon, Kimberly Sauceda, Zihan Zhu, Sergio Alvarez, Shan Zhou, Manisha Mehra, Sujan Shrestha, Prakash Sharma, James Flynn, Rebecca J. Sheesley, Sascha Usenko, Don Collins, Robert Griffin, Rice University
Abstract Number: 129
Working Group: Urban Aerosols
Abstract
Secondary organic aerosol (SOA) is a significant fraction of aerosol globally and has both anthropogenic and biogenic sources. Houston, Texas, the fourth most populous city in the U.S., is subject to a variety of industrial emissions, and previous studies emphasized different mechanisms of SOA formation between urban/industrial and suburban areas. To better understand the dynamics of SOA formation across Houston, this study (1) investigates the spatiotemporal chemical characteristics of aerosol and (2) utilizes a zero-dimensional model to estimate the SOA formation rate.
To understand the in-situ SOA formation rate in Houston, we deployed an Aerodyne high-resolution time-of-flight aerosol mass spectrometer from July to September 2022 during the TRacking Aerosol Convection interactions ExpeRiment (TRACER) field campaign. In July and August, the aerosol composition was measured for five to nine days at five locations across Houston, representing a range of suburban, urban, and industrialized locations. In September, measurements were conducted at a single industrialized site next to the Houston Ship Channel.
On average, OA contributed the most significant fraction of aerosol composition, 2.62 ± 2.49 µg/m3 (35.2%) from July to August and 7.55 ± 4.91 µg/m3 (57.8 %) in September. The diurnal pattern of OA exhibited peaks at rush hour (6 AM local time) and after times of strong solar radiation in the afternoon (~3 PM). We found three OA factors in this study using a positive matrix factorization (PMF) model: hydrocarbon-like OA (HOA), less-oxygenated OA (LO-OOA), and more-oxygenated OA (MO-OOA). Assuming the latter two represent SOA, a zero-dimensional model was used to estimate the SOA formation rate during TRACER. For MO-OOA, the largest formation rate aligned with intense photo-oxidation processes in the afternoon. For LO-OOA, however, the most significant formation rates occurred at night. The results indicate different mechanisms of daytime and nighttime SOA formation in Houston.