Investigating Plume Origins Detected by Lidar and Aircraft during a High-Ozone Event in the Chesapeake Bay Using HYSPLIT Backward Trajectories during the 2017 OWLETS Campaign

During the Ozone Water-Land Environmental Transition Study (OWLETS) in the summer of 2017, ozone, along with other species, was measured using collocated in-situ and remote sensing instruments: the NASA Langley Mobile Ozone Lidar (LMOL), one of several ozone lidars in the Tropospheric Ozone Lidar Network (TOLNet), and sensors on-board NASA’s C-23 Sherpa aircraft. The OWLETS campaign sought to understand why and how ozone tends to have higher concentrations over the Chesapeake Bay than the surrounding land. On July 20, a surface high pressure system stagnated over the southeastern US after a stalled front lifted across the Appalachian corridor, leaving favorable conditions for ozone production in the Hampton Roads area. Measurements were taken at one of the artificial islands at the Chesapeake Bay Bridge Tunnel (CBBT), our water site, and NASA Langley Research Center (LaRC) in Hampton, VA, our land site. High ozone concentrations, ranging from 60 to 100 ppbv were observed aloft, between 200 and 1800 m, and several plumes were detected by both the lidar and the Sherpa aircraft. Surface ozone concentrations were above 50 ppbv only between 15 and 18 UTC. Backward trajectory simulations were performed for multiple OWLETS observation days, including July 20, in order to better understand the origin of the plumes and the difference between ground and upper level ozone densities as observed by the different instruments. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was run using the High Resolution Rapid Refresh (HRRR) version 2 model as the main meteorological input. Other models, including the Weather Research and Forecasting – Advanced Research WRF (WRF-ARW), Global Forecast System (GFS), North American Model (NAM-12km), and the North American Regional Reanalysis (NARR) model were also used to test the sensitivity of the HYSPLIT back trajectories to the choice of meteorological model. These results suggest the buildup of ozone over the CBBT was mostly caused by local emissions, such as cars, power plants, and ship plumes, as well as photochemistry due to solar radiation prior to a sea breeze. Other sources, such as wildfire smoke originating from Canada, may contribute to observed enhancements and will be discussed. Backward trajectories for July 20 and other days are planned to be uploaded to the NASA OWLETS archive, for use by the research community at-large.