Effects of local circulations, turbulent internal boundary layers, and elevated industrial plumes on coastal ozone pollution in the downwind kaohsiung urban-industrial complex

Linyuan (LY) is a coastal station located downwind of the industrial city of Kaohsiung in southern Taiwan. This station is often affected by severe ozone pollution during sea breeze events. Intensive tethered ozone soundings were performed at this station during a 4-day ozone episode in November, 2005. Back air trajectories were also calculated to track the origins of air masses arriving at the station during the experiment. The investigation revealed complicated ozone profiles in the lower atmosphere (below 1300 m) both day and night. At night, industrial plumes forming no-ozone air layers were frequently distributed at 400 - 800 m. Mixing layers rapidly decreased from 800 -1100 m down to 200 - 350 m in the late morning hours when sea breezes and thermal internal boundary layers (TIBLs) developed. Recirculation of polluted inland air masses over the sea, the development of TIBLs, and the late development of sea-breeze events all are likely responsible for severe ozone pollution at the LY station. Elevated industrial plumes or ozone aloft above TIBLs revealed only a minor contribution to ozone pollution via a downward mixing process. Elevated ozone levels (140 -170 ppb) were often trapped within transitional layers of sea-breeze circulations at 600 - 800 m and were accompanied by ambient northerly flows parallel to the coastline, suggesting that an ozone pollution core likely formed over the west coast of Taiwan on ozone-episodic days when sea-breeze circulations developed.