Effects of vegetation on the dispersion and deposition of fine particulate matter in street canyons: from local to urban scale
Abstract
Large eddy simulation (LES) is applied to evaluate the effects of vegetation on the air quality inside street canyons. The Extended Non-periodic Domain LES for Scalar transport (ENDLESS) multi-scale approach is used to allow exploration of vegetation effects at urban scales (up to 100 canyons) while maintaining the high-resolution required to resolve flow patterns within each canyon. We consider an idealized urban environment with clean upwind air with local traffic emissions inside all canyons. In this setup, the pollution within any canyon has contributions from the local emissions within the canyon and the background level resulting from the emissions accumulated from all upwind canyons. To understand these different contributions, we investigate three emission conditions: (1) only with local traffic emissions within the canyon (the first canyon in the urban environment); (2) only with background pollution originated from the upwind canyons; (3) the combination of (1) and (2). Results show that the presence of trees has different effects on air quality inside canyons for different emission conditions. With only local traffic emissions, the increase of tree LAI increases the concentration near leeward walls and decrease the concentration near windward walls, while it decreases concentrations near both side of walls for background pollution (especially when the pollutant has a considerable deposition velocity). In an urban scale, the presence of trees reduces the buildup of background pollution, improving air quality inside canyons. Finally, a simple semi-empirical urban air quality model including dispersion and canopy deposition effects is developed, and predictions are shown to be in good agreement with LES results.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A31K3026L
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSESDE: 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 3379 Turbulence;
- ATMOSPHERIC PROCESSES