A067-0012
Investigating the Potential Causes of the Significant Decrease in the Lower-Tropospheric Baseline O3 at the U.S. West Coast During COVID-19 Pandemic

Wednesday, 9 December 2020
Poster
Seyedmorteza Amini1, Toshihiro Kuwayama1, Ryan M Stauffer2, Anne M Thompson3, Jeffrey T Abell4, Michael Ives5, Irina V Petropavlovskikh6, James H Butler7, Michael FitzGibbon1 and Elizabeth Scheehle8, (1)California Air Resources Board, Sacramento, CA, United States, (2)USRA at NASA/GSFC, Greenbelt, MD, United States, (3)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (4)Humboldt State University, Arcata, CA, United States, (5)Trinidad Head Observatory, Trinidad Head, United States, (6)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (7)NOAA Global Monitoring Laboratory, Boulder, CO, United States, (8)California Environmental Protection Agency Air Resources Board, Sacramento, CA, United States
Abstract:
Baseline ozone (O3) is defined by the U.S. Environmental Protection Agency (EPA) as the observed O3 that is uninfluenced by recent U.S. emissions. Weekly ozonesonde launches at Trinidad Head (THD), California have been providing vertical profiles of baseline O3 at the U.S. west coast since 1997. Past research has indicated that the west coast baseline O3 can directly impact O3 observed at the California surface monitoring sites, and contribute to 8-hour O3 National Ambient Air Quality Standard (NAAQS) exceedances. Baseline O3 at the west coast is mainly affected by trans-Pacific transport of O3 and stratospheric intrusions.

Due to COVID-19 pandemic, O3 precursor emissions in Asia decreased drastically. The current study analyzed the THD O3 vertical profiles and found that lower-tropospheric baseline O3 during the spring of 2020 was significantly lower than any of the 23-year historical data. To confirm this observation, a neural network algorithm, called Self-Organizing Map (SOM), was used to generate four distinct patterns of baseline O3 observed during Jan – Apr of 1998 – 2020. The results indicated that eight of the 14 profiles measured during Jan – Apr of 2020 belonged to a pattern representing the lowest average O3 levels below 4 km in altitude. The remaining six belonged to the second-lowest O3 pattern (p <0.025). For the first time in the history of the THD data, none of the profiles observed during Jan – Apr belonged to the two highest O3 patterns. A collection of observations including backward trajectories, satellite observations, and meteorological model outputs was used to investigate the causes of the significant decrease in the lower-tropospheric baseline O3 during COVID-19 pandemic. The results of this study can help regulators and researchers improve their understanding of the effects of trans-Pacific O3 transport on the west coast baseline O3, and facilitate the optimal control measures on regional anthropogenic emissions.

<< Previous Abstract | Next Abstract >>