Impact of sea breeze air masses laden with ozone on inland surface ozone concentrations: A case study of the northern coast of Taiwan

摘要

This work examines how ozone-laden sea breeze air masses contribute to inland surface ozone concentrations. The vertical distributions of ozone in sea breeze air masses and the characteristics of sea breezes are investigated using tethered ozonesondes and meteorological radiosondes, respectively, at a measurement site near the northern coast of Taiwan during 24–30 August 2003. The investigations reveal that, initially, sea breeze air masses are stable with relatively high concentrations of ozone distributed in the upper portions of the air masses. Elevated ozone layers with concentrations of 60–100 ppb were frequently observed at 500–1600 m. The growth of a thermal internal boundary layer (TIBL) inland that can bring ozone-rich air aloft in a sea breeze air mass into the growing TIBL subsequently increases the surface ozone concentrations farther inland. Accordingly, the surface ozone concentrations increase with distance inland, regardless of the photochemical production of ozone inland. A new conceptual model was presented to depict this pollution feature. According to a simple Lagrangian analysis, ozone-rich sea breeze air masses under the observed conditions generated a difference of as much as a 30 ppb between the surface ozone concentration at a near-coast location and that at a far inland location. TIBL development at a near-coast area can protect the area from fumigation of elevated ozone layers because the depth of the TIBL is limited there, such that the ozone in the elevated ozone layers cannot be brought to the ground.