ARB Research Seminar

This page updated May 23, 2019

Lidar Profiling of Ozone in the San Joaquin Valley

Photo of Andrew Langford, Ph.D,

Andrew Langford, Ph.D., NOAA ESRL CSD

June 14, 2019
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA



Air quality management strategies in California have significantly reduced health-affecting ground-level ozone (O₃) in the air that we breathe today. However, the O₃ design value in California's San Joaquin Valley (SJV) remains well above the O₃ National Ambient Air Quality Standard (NAAQS). Efforts to control ground-level O₃ are complicated by the fact that background O₃ transported over the Pacific toward California exceeds 50 parts-per-billion by volume (ppbv) or 70% of the 8-hour O₃ NAAQS in much of the Southwest during springtime. Such phenomena complicates the efforts to reduce ground-level O₃ by controlling the local O₃ precursor emissions such as oxides of nitrogen (NOₓ) and volatile organic compounds (VOCs).

In this study, the NOAA ESRL Tunable Optical Profiler for Aerosols and oZone (TOPAZ) mobile lidar was deployed in the SJV in the late spring and summer of 2016 to investigate the influence of O₃ transported aloft on ground-level O₃. The lidar was operated for an average of more than 10 hours per day during late spring (27 May to 18 June) and summer (18 July to 7 August), acquiring a total of 440 hours of lidar data during the first and the second sampling periods. This effort was part of the larger California Baseline Ozone Transport Study (CABOTS) in 2016, which was coordinated with aircraft measurements by the University of California at Davis/Scientific Aviation and the National Aeronautics and Space Administration (NASA) Ames Alpha Jet Atmospheric eXperiment (AJAX) project. This seminar will summarize the lidar observations and compare them with the surface and airborne measurements to assess their accuracy, and with the FLEXPART and NOAA ESRL GSD RAP-Chem models to estimate the influences of stratospheric intrusions, Asian pollution, and biomass burning on surface O₃ in the SJV. In particular, the TOPAZ measurements showed that emissions from the Soberanes Fire near Big Sur led to O₃ enhancements of 10-20 ppbv or more in the SJV during late July and early August, directly contributing to the highest O₃ levels measured in 2016, and likely increasing the number of exceedance days in the SJV Air Basin by about 10%.

The results from this study will help evaluate how various atmospheric conditions affect ground-level O₃ and will inform regional air quality models to better represent horizontal and vertical transport of air mass that affect O₃.

Speaker Biography

Andrew Langford is a research chemist at the Chemical Sciences Division (CSD) of National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL). He received his B.S. in Physics from Georgia Tech, and earned his Ph.D. in Physical Chemistry from University of California at Berkeley. Previously he has worked as a Postdoctoral Fellow at the University of Colorado/National Institute of Standards and Technology (NIST) Joint Institute for Laboratory Astrophysics (JILA), and worked at NOAA ESRL CSD and its NOAA Aeronomy Laboratory predecessor since 1985. Dr. Langford was jointly affiliated with Cooperative Institute for Research in Environmental Sciences at the University of Colorado from 1985 to 1992. His current focus is tropospheric chemistry and transport with an emphasis on background ozone and air quality. For more information, visit:

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