The development of the thermal internal boundary layer and its impact on ozone vertical distribution

Abstract

The evolution of the Thermal Internal Boundary Layer (TIBL) under Sea Breeze Circulation (SBC) plays a crucial role in pollutant dispersion, particularly in coastal urban areas. This study investigates the TIBL height (TIBLH) during a severe O₃ pollution episode in Hangzhou on June 5, 2016, using high-resolution simulations from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Traditional parameterizations such as the MK1992 method tend to overestimate TIBLH by neglecting urban heat island (UHI) effects and he inland enhancement of momentum by the SBC. To address these limitations, we develop an improved scheme, HS 2024, which explicitly incorporates both the UHI-driven thermal convection and SBC-induced mechanical turbulence. Compared to MK 1992, HS2024 more accurately captures the diurnal evolution of TIBLH and its modulation of vertical O₃ transport. As the SBC progresses inland, the TIBLH gradually decreases and forms a capping layer that traps pollutants in the lower troposphere, exacerbating near-surface O₃ concentrations. These findings underscore the importance of accounting for both thermal and dynamical processes in TIBLH estimation and provide a more physically grounded framework for air quality prediction in complex coastal cities.