Sea-Land Difference of the Atmospheric Boundary Layer Structure and its Influence on Pm2.5 — Observation and Numerical Simulation

Abstract

A comprehensive observation was conducted for a whole year from July 2017 to July 2018 on the west coast of the Bohai Sea. Along the sea-coast-inland area, three sites were set and equipped with aerosol lidar, fast response instruments and the automatic meteorological station. Sea-land difference of the atmospheric boundary layer structure and its influence on PM2.5 were analyzed based on observation and numerical simulation. Affected by the sea-land difference of heat capacity and the sensible heat flux, the PBLH over the sea was 330 m higher than that over the land in winter, but in summer, the opposite was observed. There is no significant difference in the diurnal variation of turbulent energy between winter and summer over the sea. Instead, the turbulent energy over the land in summer was remarkably higher than that in winter. The duration of sea breeze was 10~ hours in summer and merely 3 hours in winter. The averaged intensity and influence distance of sea breeze were -2°C and 40 km in summer and -1°C and 5~10 km in winter. The diurnal variation of PM2.5 vertical profiles over the sea, coast and land was different. At the height of 200 to 600 meters, the concentration over the coast was higher than that over the land on winter night. But the opposite was observed on summer nights. During the typical sea-land breeze episode, there was an obvious temperature gradient between sea and land from surface to 400 m. As the sea breeze pushed inland, temperature inversion was formed along the way and vertical diffusion was suppressed, forming a high concentration center of pollutants. The results can deepen the understanding of the structure of sea- land atmospheric boundary layer, and provide support for the prediction of heavy pollution episode.

Keywords: Sea-land difference, PM2.5 profile, Sea breeze, Turbulence, Field observation, Numerical simulation