. Boundary layer entrainment of transported ozone layers observed with lidar during the CABOTS and FAST-LVOS studies

Abstract
Recently, two air quality campaigns were conducted in the southwestern United States to study the impact of transported ozone, stratospheric intrusions, and fire emissions on ground-level ozone concentrations. The California Baseline Ozone Transport Study (CABOTS) took place in May-August 2016 covering the central California coast and San Joaquin Valley, and the Fires, Asian, and Stratospheric Transport Las Vegas Ozone Study (FAST-LVOS) was conducted in the greater Las Vegas, Nevada area in May-June 2017. The NOAA truck-based Tunable Optical Profiler for Aerosols and oZone (TOPAZ) lidar was a key component of both studies and was deployed at the Visalia Municipal Airport during CABOTS and the North Las Vegas Airport during FAST-LVOS. About 1000 hours of ozone and aerosol profile data from near the surface to 5-8 km above ground level (AGL) were collected with the TOPAZ lidar in both studies combined. The autonomous NOAA MicroDoppler wind lidar was deployed next to TOPAZ during part of CABOTS and for the entire FAST-LVOS study to provide continuous observations of vertical wind speed, turbulence, and mixing height. The TOPAZ observations revealed a complex vertical ozone structure during both studies, including distinct high-ozone layers in the free troposphere associated with stratospheric intrusions, long-range transport from Asia, wildfire plumes, and regional pollution transport. The high-resolution, continuous TOPAZ ozone profile data enabled us to directly observe to what degree these elevated ozone layers were entrained into the boundary layer. Mixing heights in the San Joaquin Valley during CABOTS were generally below 1 km AGL, while boundary layer heights in Las Vegas during FAST-LVOS routinely exceeded 3 km AGL and occasionally reached up to 5 km AGL. Consequently, boundary layer entrainment was more often observed during FAST-LVOS, while most elevated ozone layers passed untapped over the San Joaquin Valley during CABOTS. We will show several examples of entrainment and mixing to the surface of elevated ozone layers, quantify their impact on ground-level ozone concentrations, and contrast the different boundary layer regimes in the San Joaquin Valley and Las Vegas and their effect on entrainment.