California Air Resources Board

Principal Investigator/Author: Qi Zhang

Contractor: University of California, Davis

Contract number: 22RD038

Project Status: Active

Relevant CARB programs: California State Implementation Plans, Criteria Air Pollutants

Topic areas: State Implementation Plans (SIPs), Particulate Matter (PM), PM2.5

Research Summary:

The San Joaquin Valley (SJV) in California consistently encounters air quality issues associated with particulate matter (PM) and frequently violates the 24-hr PM2.5 National Ambient Air Quality Standards (NAAQS). The SJV is currently implementing several PM2.5 control strategies to achieve air pollution reduction goals as laid out in the latest State Implementation Plan (SIP) that guides the SJV to achieve PM2.5 reduction milestones by the end of 2025. The Senate Bill (SB) 1383 also mandates the reduction of anthropogenic black carbon emissions, a component of PM2.5, by 50% below 2013 levels by 2030. To evaluate the progress of ongoing air pollution mitigation strategies, it is necessary to link continuous, long-term measurements of ambient PM2.5 concentration and chemical composition in the SJV with the changing influences of primary emission sources, chemical pathways, and meteorological conditions.

This project aims to gain a comprehensive understanding of the primary emission sources, chemical pathways, and meteorological conditions that affect ambient PM2.5 levels in the SJV. To achieve this goal, the University of California, Davis (UCD) research team will collect sub-hourly measurements of non-refractory PM2.5 concentration and chemical composition using an Aerosol Chemical Speciation Monitor (ACSM) at Fresno, CA and Bakersfield, CA for the next three consecutive years. The project will combine the ACSM data with co-located measurements of black carbon, volatile organic compounds, and meteorological conditions collected by the California Air Resource Board (CARB), to conduct advanced analyses that will help elucidate PM2.5 characteristics in the SJV and identify the major drivers affecting ambient PM2.5 levels and their constituents. UCD will also conduct a month-long intensive measurement campaign in Fresno during the fall/winter of 2023 using two state-of-the-science real-time mass spectrometers. This data will be used to study the contribution of various primary emission sources (e.g., mobile, biomass burning, cooking, and agricultural activities) to ambient PM2.5. The research team will examine the influence of secondary formation pathways and nocturnal residual-layer chemistry on the ambient concentrations and temporal patterns of critical secondary inorganic and organic PM species in the SJV. Lastly, they will synergistically compare these results to the findings from CARB-funded contract number 17RD008 to inform CARB, the local government, and the community of the effects of ongoing PM2.5 control strategies in the SJV. Project results will significantly advance the understanding of the complex mechanisms that contribute to elevated ambient PM2.5 levels in the region and aid in the development and refinement of future SJV SIPs and SB1383 initiatives.

Keywords: particulate matter, PM, San Joaquin Valley, SJV, SB 1383, black carbon emissions, PM reduction, air pollution, chemical composition, meteorological conditions, chemical pathway