A CFD modeling study of the impacts of NOx and VOC emissions on reactive pollutant dispersion in and above a street canyon
A CFD modeling study of the impacts of NOx and VOC emissions on reactive pollutant dispersion in and above a street canyon
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DOI：
10.1016/j.atmosenv.2011.10.024
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发表时间：
2012
影响因子：
5
通讯作者：
K. Kwak;Jong‐Jin Baik
中科院分区：
文献类型：
--
作者：
K. Kwak;Jong‐Jin Baik
A computational fluid dynamics (CFD) model that includes the carbon bond mechanism IV (CBM-IV) is developed and used to investigate reactive pollutant dispersion in and above a street canyon with an aspect ratio of 1. Fourteen emission scenarios of NOxand volatile organic compounds (VOCs) are considered. Dispersion types are classified into NO-type, NO2-type, and O3-type dispersion that exhibit concentration maxima at the street bottom, near the center of the street canyon, and above the street canyon, respectively. For the base emission scenario, the number of reactive species is 9 in the NO-type dispersion, 10 in the NO2-type dispersion, and 15 in the O3-type dispersion. As the NOxemission level decreases or the VOC emission level increases, some species in the O3-type dispersion are shifted to the NO2-type dispersion. The VOC-to-NOxemission ratio is found to be an important factor in determining the transition of dispersion type. In this transition process, OH plays a key role through a radical chain including HO2, RO, and RO2. Because of their high OH reactivities, XYL (xylene) and OLE (olefin carbon bond) among VOCs are largely responsible for the transition of dispersion type. The O3sensitivity is examined by reducing NOxor VOC emission level by a half. Because the NO titration of O3is more pronounced than the NO2photolysis and the radical chain process in the street canyon, the O3concentration therein is negatively correlated with the NOxemission level and weakly correlated with the VOC emission level. As a result, the street canyon is a negatively NOx-sensitive regime.
