Project at a Glance

Title: Lidar profiling of ozone above the central San Joaquin Valley during the California Baseline Ozone Transport Study (CABOTS)

Principal Investigator / Author(s): Langford, Andrew

Contractor: National Oceanic & Atmopsheric Administration (NOAA)

Contract Number: 15RD012

Research Program Area: Atmospheric Processes

Topic Areas: Ambient Air Quality Standards, Area Sources, Field Studies, Modeling, Transport


Ground-level ozone (O3) is harmful to human health and the environment, and is regulated under the Clean Air Act (CAA). The San Joaquin Valley (SJV) is classified as an extreme O3 non-attainment area for the 8-hour O3 National Ambient Air Quality Standard (NAAQS). Although studies have shown that local and regional photochemical production is the dominant source of the high ground-level O3 in the SJV, it has been determined that O3-rich lower stratospheric air can sometimes descend and entrain transported Asian pollution and biomass burning plumes to the surface. To evaluate the impact of long-range transport, stratospheric intrusion, and biomass burning on ground-level O3 in the SJV, this project conducted measurements of O3 and particulate backscatter profiles above the SJV using the Tunable Optical Profiler for Aerosols and oZone (TOPAZ) mobile lidar. The measurements were conducted as part of the 2016 CABOTS coordinated by CARB, which aimed to investigate the influence of O3 transported aloft on ground-level O3 in the SJV. This effort also coincided with additional in-situ data collected by researchers from the University of California at Davis (UCD), Scientific Aviation, and NASA Ames Research Center. Furthermore, the TOPAZ data was paired with NOAA ESRL Global Systems Division (GSD) RAP-Chem and FLEXPART models to further evaluate the impact of transported O3 in the SJV. The resulting data revealed elevated O3 layers between 4 and 6 km above the SJV, consistent with biomass burning, transport from Asia, and descent from the lower stratosphere. However, most of these layers passed over the Sierra Nevada since the boundary layers in the SJV were too shallow to capture the O3 transported aloft during the measurement campaign. A few descending events were captured that decreased ground-level O3 due to displacement of more polluted surface air. Longer, more continuous measurements are necessary to investigate the frequency of impacts on an annual basis especially when the photochemical production of O3 at the surface is less prominent. Analysis of the data during a wildfire event (Soberanes Fire near Big Sur) suggested that ground-level O3 increased in the central SJV by 10-20 parts-per-billion by volume (ppbv) or more each day during the first two weeks after the fire started, including the highest O3 days in 2016. The emissions from this fire may be responsible for the 10 percent increase in the number of exceedance days in the SJV in 2016.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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