Numerical simulation and sensitivity analysis of atmospheric environmental capacity and air pollution processes in Fen River Valley
Recent years have seen rapid industrialization and urbanization in China,leading to increased urban energy consumption and atmospheric pollutant emissions,posing severe air pollution challenges in some cities.The Fen River Valley,a critical area for air pollution prevention and control,experiences significant influences on pol-lutant dispersion within the atmospheric boundary layer due to its distinctive basin topography and the urban heat island effects of its large internal cities.This study employs the WRF-Chem model to investigate a severe pollution event in the Fen River Valley and Taiyuan City in January 2015.The study includes numerical simulations of the pollution process,observational validations,and terrain sensitivity experiments.It utilizes boundary layer height and wind speed to establish the Atmospheric Environment Capacity Index(AECI),quantifying the atmospheric dispersion capability.This index,along with the spatiotemporal distribution of PM2.5 concentrations,assesses the impact of surrounding terrain on local air pollution,providing a scientific basis for air pollution control policy for-mulation.Results show that atmospheric boundary layer circulation and pollutant transport in Taiyuan City and the surrounding Fen River Valley are influenced by weather systems,terrain,and urbanization.Terrain-induced circu-lation intensity significantly outweighs the urban heat island circulation in Taiyuan and markedly impacts its de-velopment.At night,mountainous terrain confines the boundary layer height within 200 to 400 m,while a weak-ened terrain sensitivity group shows only about 100 m.However,during the day,mountains compress the boundary layer height by more than 400 m in the sensitive group.Thus,to some extent,mountains limit urban atmospheric capacity,exacerbating the accumulation of near-surface air pollutants and deteriorating air quality.This is primarily evidenced by the experiment's terrain-sensitive group,where weakening the surrounding valley's topographic fea-tures in Taiyuan slows the PM2 5 concentration rise during the accumulation phase,aligning with the Fen River Valley dynamics.Terrain is identified as a primary factor affecting the distribution of atmospheric pollutants.The Fen River Valley's north-south orientation and its broader southern section influence regional atmospheric capaci-ty,dictated by prevailing wind directions.When the dominant wind direction aligns with the valley's orientation,the increased wind speed due to the venturi effect enhances the valley's atmospheric capacity,facilitating pollutant dispersion and clearance.Conversely,when the dominant wind direction is perpendicular to the valley,mountainous terrain suppresses near-surface wind speeds and forms lower wind zones at the interface of the valley and mountains,significantly reducing the area's atmospheric capacity.This reduction strongly correlates with near-surface pollutant concentrations,with a correlation coefficient of 0.74;this correlation drops to 0.21 in the terrain-sensitive group,further underscoring the significant impact of terrain on air pollution processes.Overall,the sur-rounding mountains inhibit urban atmospheric capacity,particularly by accelerating the concentration increase dur-ing the pollutant accumulation phase.However,the specific mechanisms are complex and vary with different wind directions and diurnal cycles,suggesting that future research could further investigate the interactions between me-teorological and topographical factors and propose more effective environmental management strategies.
Fen River Valleyatmospheric environment numerical simulationWRF-Chemterrain and land usemountain-valley breeze
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