Modeling the Impacts of City-Scale “Ventilation Corridor” Plans on Human Exposure to Intra-Urban PM2.5 Concentrations

Chao Liu,Sen Huang,Jingwei Guo,Qian Shu

doi:10.3390/atmos12101269

Abstract

Increasingly, Chinese cities are proposing city-scale ventilation corridors (VCs) to strengthen wind velocities and decrease pollution concentrations, although their influences are ambiguous. To assess VC impacts, an effort has been made to predict the impact of VC solutions in the high density and diverse land use of the coastal city of Shanghai, China, in this paper. One base scenario and three VC scenarios, with various VC widths, locations, and densities, were first created. Then, the combination of the Weather Research and Forecasting/Single-Layer Urban Canopy Model (WRFv.3.4/UCM) and Community Multiscale Air Quality (CMAQv.5.0.1) numerical simulation models were employed to comprehensively evaluate the impacts of urban spatial form and VC plans on PM2.5 concentrations. The modeling results indicated that concentrations increased within the VCs in both summer and winter, and the upwind concentration decreased in winter. These counter-intuitive results could be explained by decreased planetary boundary layer (PBL), roughness height, deposition rate, and wind speeds induced by land use and urban height modifications. PM2.5 deposition flux decreased by 15–20% in the VCs, which was attributed to the roughness height decrease for it weakens aerodynamic resistance (Ra). PBL heights within the VCs decreased 15–100 m, and the entire Shanghai’s PBL heights also decreased in general. The modeling results suggest that VCs may not be as functional as certain urban planners have presumed.

Highlights

Chinese cities have proposed varieties of urban plans, strategies, and management plans in response to severe intra-urban fine particulate (PM2.5) pollution in past years [1,2].Among them, city-scale ventilation corridors (VCs) are an aggressive but popular proposal [3]
PM2.5 pollution maps were created in CMAQv.5.0.1, incorporating the meteorology map generated with WRFv.3.4-Urban Canopy Model (UCM)
Each VC scenario was assessed by WRFv.3.4-UCM and CMAQv.5.0.1 to simulate PM2.5 values within VCs and the whole city

Summary

Introduction

City-scale ventilation corridors (VCs) are an aggressive but popular proposal [3]. Certain megacities, such as Shanghai, Beijing, and Nanjing, have started to plan urban VCs to mitigate air pollution concentrations. The urban-scale VCs have not been well identified, there have been many references studying the street canyon’s effects on air pollution variations [4,5,6]. The VCs’ influence on urban ventilation and air pollution needs to be adequately evaluated to support plans and implementations. This paper, as one of the earliest attempts, investigates VC’s effectiveness on air pollution influences at the urban level

Methods

Results

Discussion

Conclusion