Land-sea difference of the planetary boundary layer structure and its influence on PM_2.5 - Observation and numerical...

A comprehensive set of observations were collected along a sea-coast-inland area. According to these observations, the planetary boundary layer heights (PBLH) during winter and summer for sampling locations in sea, coast, and inland areas were 737 m, 483 m and 372 m, and 450 m, 645 m and 646 m, respectively. Little seasonal difference was observed for the daily variation of sensible heat flux over the sea, with the maximum of 55 W/m² at 12:00 in winter and 27 W/m² at 13:00 in summer. The duration of sea breeze was ∼10 h in summer and only 3 h in winter, extended to inland area ∼ 50 km and upward 920 m vertically. PM_2.5 at coastal area was about 5 μg/m³ higher than inland during summer afternoon. Over the sea, PM_2.5 mainly concentrated below 200 m in winter, increased with height at night and decreased with height in the morning below 300 m in summer. A typical land-sea breeze episode was analyzed with observed and simulated result. According to the observed data, the sea breeze extended to inland ∼50 km and upward 300 m vertically. From the simulating result, there was a clear temperature gradient between sea and land from surface to 400 m, when influenced by the sea breeze, the wind and temperature profiles showed different characteristics, and forming a high concentration center of PM_2.5 at 300 m. These results provide insights into the structure of land-sea planetary boundary layer, and provide support for the prediction of heavy pollution episode.