Land-sea difference of the planetary boundary layer structure and its influence on PM2.5-Observation and numerical simulation

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 ob-served 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. PM2.5 at coastal area was about 5 mu g/m3 higher than inland dur-ing summer afternoon. Over the sea, PM2.5 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 char-acteristics, and forming a high concentration center of PM2.5 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.

Automated summary

Observations were collected along a sea-coast-inland area, showing that the planetary boundary layer heights varied across different locations and seasons. The sea breeze had little seasonal difference in the daily variation of sensible heat flux, and the duration and extension of sea breeze differed between summer and winter. PM2.5 concentrations also varied between coastal and inland areas, with different vertical profiles in winter and summer. The analysis of a land-sea breeze episode revealed the impact on wind and temperature profiles, resulting in a high concentration center of PM2.5 at a certain height. These findings provide insights into the structure of the land-sea planetary boundary layer and support the prediction of heavy pollution episodes.