Analysis of Pollutant Dispersion in a Realistic Urban Street Canyon Using Coupled CFD and Chemical Reaction Modeling

Abstract

Studies in actual urban settings that integrate chemical reaction modeling, radiation, and particular emissions are mandatory to evaluate the effects of traffic-related air pollution on street canyons. In this paper, airflow patterns and reactive pollutant behavior for over 24 h, in a realistic urban canyon in Osaka City, Japan, was conducted using a computational fluid dynamics (CFD) model coupled with a chemical reaction model (CBM-IV). The boundary conditions for the CFD model were obtained from mesoscale meteorological and air quality models. Inherent street canyon processes, such as ground and wall radiation, were evaluated using a surface energy budget model of the ground and a building envelope model, respectively. The CFD-coupled chemical reaction model surpassed the mesoscale models in describing the NO, NO2, and O3 transport process, representing pollutants concentrations more accurately within the street canyon since the latter cannot capture the local phenomena because of coarse grid resolution. This work showed that the concentration of pollutants in the urban canyon is heavily reliant on roadside emissions and airflow patterns, which, in turn, is strongly affected by the heterogeneity of the urban layout. The CFD-coupled chemical reaction model characterized better the complex three-dimensional site and hour-dependent dispersion of contaminants within an urban canyon.

A Review on the Dispersion and Distribution Characteristics of Pollutants in Street Canyons and Improvement Measures

“…The three-dimensional landscape pattern of a city block is an important factor that determines the air flow movement and the dispersion effect of air pollutants in the block and affects the quality of the air environment inside the block [51]. Unreasonable spatial arrangement and structure of urban streets and canyons often cause local air pollution.…”

Impacts of the Tree Canopy and Chemical Reactions on the Dispersion of Reactive Pollutants in Street Canyons

“…The calculation domain and period used was the same as that in Gonzalez Olivardia et al [13]. The calculation domain was developed based on the city of Umeda-Shinmichi (34.70 • N, 135.50 • E), Osaka City, Japan.…”

“…Lateral boundary conditions of the wind velocity, air temperature, and pollutant concentrations were derived from the weather research and forecasting (WRF) model and the community multiscale air quality (CMAQ) modeling system, the same as in Gonzalez Olivardia et al [13]. The physics parameterizations and input data for WRF/CMAQ were the same as those used by Shimadera et al [36].…”

“…To understand the flow field and the pollutant concentrations within a canyon, several tools can be utilized including field measurements [8], wind tunnel experiments [1,3,[6][7][8][9][10], and computational fluid dynamics (CFD) simulations [1,[4][5][6][7][8][9][10][11][12][13][14][15][16]. The field measurements provide the most reliable data about the actual behavior of pollutants dispersed in the canyon, but it is difficult to control the relevant conditions such as the aspect ratio, building shapes, wind velocity, wind direction, and so forth.…”

RANS model calibration using stochastic optimization for accuracy improvement of urban airflow CFD modeling

“…Increasing applications of computational fluid dynamics (CFD) in the urban studies reflects on its importance in research and practical engineering applications (Blocken, 2014;Jiru and Bitsuamlak, 2010). Different aspects of airflow in urban environment, including pedestrian level wind comfort (Blocken et al, 2016;Fadl and Karadelis, 2013;Iqbal and Chan, 2016;Mirzaei and Haghighat, 2011;Serteser and Karadag, 2018;Tsang et al, 2012;Wang et al, 2019;Yoshie et al, 2007), building energy (Allegrini et al, 2015;Charisi et al, 2019;Cook et al, 2008;Fan and Ito, 2012;Malys et al, 2015;Mochida et al, 2006b;Zhai et al, 2002;Zhang et al, 2018), pollution dispersion (Abbassi et al, 2019;Gonzalez Olivardia et al, 2019;Haghighat and Mirzaei, 2011;Longo et al, 2019;Luo et al, 2016;Tominaga andStathopoulos, 2011, 2010;Yoshie et al, 2011), and urban heat island (Allegrini et al, 2015;Hien et al, 2012;Kawamoto, 2016;Mirzaei et al, 2015;Priyadarsini, 2009) are the main subject areas tackled by CFD models.…”