Large-Eddy Simulation on urban-scale air quality modeling in coastal areas

Abstract

Studies exploring the turbulent structure of the planetary boundary layer (PBL) over complex topographies are very limited because of the lack of available observations and difficulty of highly resolved simulation. In this study, micro-meteorological and turbulent characteristics over complex coastal areas were investigated based on high spatial-temporal resolution by using the Weather Research and Forecasting–Large Eddy Simulation (WRF-LES) model. Then, the simulations were compared to comprehensive observations obtained at the Boseong Standard Weather Observatory (BSWO), which is equipped with various observation facilities, such as a meteorological observation tower with a height of 307 m, and aiding ground-based remote sensing measurements used for PBL research. The comparison between the WRF-LES model results and the measurements by the wind lidar system at the BSWO showed that the LES approach in this study reproduced the spatial/vertical wind field structure and land-sea wind circulation distinctly better than the conventional PBL schemes. High turbulent kinetic energy (TKE) was observed near the surface level at night due to the increased nocturnal shear production following the evolution of land and mountain breezes. The calculated TKE from WRF-LES model was applied to identify the mixing intensity based on the mixing length and eddy diffusion coefficient within the boundary layer, and then those were evaluated with the observed extinction coefficient from the aerosol Micro-Pulse Lidar system (MPL). In addition, the planetary boundary layer height (PBLH) at night was explored by using the TKE threshold method combined with the bulk Richardson number threshold method for the daytime PBLH. Compared with the observed value from a ceilometer at the BSWO, we found that the TKE threshold method proposed in this study could yield highly accurate PBLH values, especially at night. It is also expected that the enhanced application of WRF-LES like to this study can lead to understanding and prediction with the high confidence for much detail and accurate spatiotemporal turbulent structure over complex coastal areas, which will contribute to more comprehensive air quality modeling studies. Understanding the turbulent structure and mixing processes within the PBL over complex coastal areas is critical for accurately simulating pollutant transport and dispersion. The integration of the WRF-LES model with observational data provides a robust framework for capturing the intricate interactions between local meteorological conditions and emissions in coastal industrial regions. Industrial complexes in coastal areas significantly impact air quality due to emissions of hazardous chemicals compounded by local circulation. This study introduces a WRF-LES-CMAQ modeling system designed for high-resolution air quality simulations in a coastal industrial complex. The LES framework explicitly resolves near-surface turbulence, improving meteorological field accuracy, including wind, temperature, and PBLH, compared to traditional PBL parameterization. A modified horizontal diffusion term in the CMAQ system was implemented to address pollutant dispersion under fine grid resolution. Evaluation using SIJAQ 2022 campaign data demonstrated strong model performance in reproducing ground-level pollutant concentrations and tropospheric NO2 distributions. The model effectively captured the inland dispersion of NO2 driven by sea breeze, highlighting the spatiotemporal variability of emissions from the industrial complex. Sensitivity to uncertainties in the emissions inventory was noted, raising the need for accurate emissions allocation. High-resolution simulations revealed critical atmospheric dynamics, such as pollutant trapping by eddies and the persistence of PM2.5 in the shallow boundary layer over coastal areas. These findings underscore the LES framework’s ability to represent turbulence-driven behavior and detailed pollution patterns in complex terrains. The WRF-LES-CMAQ system demonstrates its utility for air quality assessments in regions with localized meteorological and topographical features. By providing detailed insights into pollutant transport and dispersion, the model supports improved environmental management and air quality prediction, offering valuable applications for industrial and coastal areas globally.