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Investigating PM2.5 Composition and Sources in the San Joaquin Valley of California Using a ToF-ACSM with the Capture Vaporizer
Peng Sun, Ryan Farley, Lijuan Li, Deepchandra Srivastava, Christopher Niedek, Jianjun Li, Ningxin Wang, Christopher Cappa, Sally Pusede, Zhenhong Yu, Philip Croteau, QI ZHANG, University of California, Davis
Abstract Number: 481
Working Group: Urban Aerosols
Abstract
The San Joaquin Valley (SJV) of California has suffered persistent particulate matter (PM) pollution despite many years of control efforts. To further understand the chemical drivers of this problem and to support state implementation plan (SIP) development for PM, a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) outfitted with a PM2.5 lens and a new capture vaporizer has been deployed at the Fresno-Garland air monitoring site of the California Air Resource Board (CARB) since Oct. 2018. The instrument measured non-refractory (NR) species in PM2.5 continuously at 10 min time resolution. In this study, data acquired from Oct. 2018 to May 2019 were analyzed to investigate the chemical characteristics, sources and atmospheric processes of PM2.5 in the SJV. Comparisons of the ToF-ACSM measurement with various co-located aerosol instruments show good agreements. The inter-comparisons indicated that PM2.5 in Fresno was dominated by submicron particles during the winter whereas refractory species were found to account for a major fraction of PM2.5 mass during the autumn associated with elevated PM10 loadings. A rolling window positive matrix factorization (PMF) analysis of organic aerosol (OA) mass spectra was performed using the Multilinear Engine (ME-2) algorithm. Three distinct OA factors were resolved, including a hydrocarbon-like HOA, a biomass burning BBOA, and an oxygenated OOA. There were significant seasonal variations in PM2.5 composition and sources. During the winter, residential wood burning and oxidation of nitrogen oxides were major contributors to the occurrence of haze episodes with PM2.5 dominated by BBOA and nitrate. In autumn, agricultural activities and wildfires were found to be the main cause of PM pollution. PM2.5 concentrations decreased significantly after spring and were dominated by OOA during March to May. Our results highlight the importance of using seasonally dependent control strategies to mitigate PM pollution in the SJV.