California Air Resources Board

SACRAMENTO - This summer dozens of scientists from State and federal agencies and universities are using four different aircraft with more than 200 flight hours, balloons that measure ozone aloft, and a laser-based instrument that measures ozone above the ground up to 12,000 feet, to investigate ozone which enters California from the Pacific Ocean. The three-month research project (mid-May to mid-August) will help scientists learn if ozone entering the state from the Pacific has an effect on air quality at the surface in the San Joaquin Valley.  

As California continues to reduce local sources of ozone, ozone entering the state from the Pacific makes up a larger fraction of measured ozone levels.  Current ozone levels in the San Joaquin Valley are predominantly caused by local emissions, but as air quality standards become lower, any contribution from global ozone levels needs to be understood. The California Baseline Ozone Transport Study (CABOTS) will investigate the concentrations of ozone aloft at a site on the Northern California coast and the role that ozone hundreds -- or even thousands -- of feet above the surface can play in surface measurements in the San Joaquin Valley.

“California must continue to achieve significant new reductions in ozone emissions to achieve federally mandated health-based standards,” said California Air Resources Board (CARB) Chair Mary D. Nichols. “Science is key to helping us understand what causes areas of our state like the San Joaquin Valley to exceed the ozone standard. By combining resources with NOAA, NASA and San Jose State, California will get new data to answer important questions about air pollution that comes into our state from across the globe.” 

Recent health research has led the U.S. Environmental Protection Agency to adopt a lower, more health protective ozone standard.  At the same time, increasing industrialization in Asia and global emissions of methane has led to higher ozone concentrations entering California from the west. Actions to decrease climate change, such as California’s proposed Short-Lived Climate Pollutant Reduction Strategy and the U.S. EPA’s actions to curb methane emissions, will help to decrease global ozone levels.

The foundation of CABOTS is two CARB research contracts totaling $400,000, but coordination with other ongoing CARB and federal studies will result in measurements which would likely cost well over $1 million to replicate. 

The foundational CABOTS projects measure ozone vertical profiles at two locations during the late spring and summer of 2016:

• A contract with San Jose State University, “Improved Understanding of the Magnitude of Trans-Pacific Long Range Transported Ozone Aloft at California’s Coast,” provides near daily ozonesonde launches from the UC Davis Bodega Marine Laboratory. An ozonesonde is a balloon which measures ozone from the surface to more than 10 kilometers above the ground. Data collected from this project will help researchers better quantify the magnitude and temporal variations in measured ozone concentrations entering California.

• A contract with the National Oceanic and Atmospheric Administration (NOAA), “Lidar Profiling of Ozone in the San Joaquin Valley,” uses a surface-based ozone lidar to provide ozone profiles in the San Joaquin Valley for three weeks in both the spring and summer of 2016. Lidar is a technology that uses a laser to measure ozone concentrations in a vertical column up to 5 kilometers above the ground. The data will help CARB to better characterize the ozone vertical profile and its temporal variation in the San Joaquin Valley, and to understand the vertical mixing of ozone aloft down to the surface.

Additional measurements that will happen during the study period which are expected to enhance our understanding of the impact of long-range transported ozone pollution are: 

• Daily aircraft flights between 4 and 6 a.m. over Fresno and Bakersfield between June and September. Part of CARB’s Aircraft Pilot Observation program, the flights make continuous measurements of ozone up to 3,000 meters above ground.

• A second CARB-funded aircraft project aims to characterize the ozone content of the lower atmosphere from dawn to early evening at Fresno, Bakersfield and points in between. Approximately 10 days of flights will happen this spring and summer.

• The Alpha Jet Atmospheric Experiment (AJAX) project at NASA Ames Research Center makes regular measurements of ozone and other trace gases over California.  In support of CABOTS, AJAX will sample air composition offshore and between the locations of the ground-based and balloon measurements.  

• CABOTS will also benefit from data collected by NASA’s DC-8 flying laboratory. Two flights, on Friday, June 17, and Saturday, June 18, part of the NASA Student Airborne Research Program, will target the atmosphere above the SJV.

• Ozone measurements at Chews Ridge (a site in the Coastal Range southeast of Monterey) funded by the San Joaquin Valley Air Pollution Control District will provide ozone data at a high elevation near the coast and west of the lidar measurements.