Journal
BUILDING SIMULATION
Volume 15, Issue 7, Pages 1227-1241Publisher
TSINGHUA UNIV PRESS
DOI: 10.1007/s12273-021-0795-6
Keywords
street canyon; viaduct; reactive pollutant; photochemical reaction; CFD
Categories
Funding
- National Key Research and Development Plan (Key Special Project of Intergovernmental National Scientific and Technological Innovation Cooperation) [2019YFE0197500]
- National Natural Science Foundation of China [51778511, 51778253]
- European Commission H2020 Marie S Curie Research and Innovation Staff Exchange (RISE) award [871998]
- Hubei Provincial Natural Science Foundation of China [2018CFA029]
- Key Project of ESI Discipline Development of Wuhan University of Technology [2017001]
- Fundamental Research Funds for the Central Universities [2019IVB082]
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This study investigated the diffusion of reactive pollutants emitted by motor vehicles in a 2-dimensional street canyon by using computational fluid dynamics (CFD) method. The presence of a viaduct was found to change the flow field structure in the street canyon and increase pollutant concentrations. The influence of the viaduct on the concentration of reactive pollutants was significantly larger than that of chemical reactions.
In this paper, the influences of the ambient wind speed and the height and width of a viaduct in a 2-dimensional street canyon on the diffusion of reactive pollutants emitted by motor vehicles were investigated using computational fluid dynamics (CFD) method. Pollutants were treated as reactive by including a NO-NO2-O-3 photochemical reaction mechanism in the simulation. The Reynolds-averaged Navier-Stokes (RANS) k-epsilon turbulence model and the discrete phase model were used to simulate the airflow movement and the concentration distribution, respectively, of the reactive pollutants in the street canyon. Three indices, i.e., the chemical reaction contribution of NO (CRCNO), the chemical reaction contribution of NO2(CRCNO2), and the O-3 depletion rate, were used to evaluate the relative importance of the photochemical reactions. It was found that the presence of a viaduct changed the flow field structure in the street canyon. The CRCNO and CRCNO2 decreased from the windward side to the leeward side of the canyon. The maximum values of the CRCNO and CRCNO2 were observed at the pollution source (x = 245 m) due to the influence of a clockwise vortex in the street canyon. As the height and width of the viaduct increased, concentration of the ground pollutants and the O-3 depletion rate increased. The O-3 depletion rate was much higher on the leeward side (90%) than on the windward side. The pollutant concentrations after the reaction were twice as high with the viaduct as without the viaduct when the viaduct height was the same as the building height. The viaduct had a significantly larger influence on the concentration of the reactive pollutants than the chemical reactions. The O-3 depletion rate in the canyon and the pollutant concentrations decreased as the ambient wind speed increased, whereas the CRCNO2 increased.
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