Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry

Research output: Contribution to journal › Article › peer-review

Standard

Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry. / Zhong, Jian; Cai, Xiaoming; Bloss, William.

In: Environmental Pollution, 12.02.2017.

Research output: Contribution to journal › Article › peer-review

Harvard

Zhong, J, Cai, X & Bloss, W 2017, 'Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry', Environmental Pollution. https://doi.org/10.1016/j.envpol.2017.01.076

APA

Zhong, J., Cai, X., & Bloss, W. (2017). Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry. Environmental Pollution. https://doi.org/10.1016/j.envpol.2017.01.076

Vancouver

Zhong J, Cai X, Bloss W. Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry. Environmental Pollution. 2017 Feb 12. https://doi.org/10.1016/j.envpol.2017.01.076

Author

Zhong, Jian ; Cai, Xiaoming ; Bloss, William. / Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry. In: Environmental Pollution. 2017.

Bibtex

@article{baedb070e33a4e99b85133d92d2c3117,
title = "Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry",
abstract = "A large eddy simulation (LES) model coupled with O3-NOx-VOC chemistry is implemented to simulate the coupling effect of emissions, mixing and chemical pre-processing within an idealised deep (aspect ratio = 2) urban street canyon under a weak wind condition. Reactive pollutants exhibit significant spatial variations in the presence of two vertically aligned unsteady vortices formed in the canyon. Comparison of the LES results from two chemical schemes (simple NOx-O3 chemistry and a more comprehensive Reduced Chemical Scheme (RCS) chemical mechanism) shows that the concentrations of NO2 and Ox inside the street canyon are enhanced by approximately 30-40% via OH/HO2 chemistry. NO, NOx, O3, OH and HO2 are chemically consumed, while NO2 and Ox (total oxidant) are chemically produced within the canyon environment. The within-canyon pre-processing would increase oxidant fluxes released from the canyon to the overlying boundary layer, and this effect is more crucial for deeper street canyons (as found in many traditional European urban centres) than shallower (lower aspect ratio) streets. There is clear evidence of distinct behaviours for emitted chemical species and entrained chemical species, and positive (or negative) values of intensities of segregations are found between pairs of species with a similar (or opposite) behaviour. The simplified two-box model underestimated NO and O3 levels, but overestimated NO2 levels for both the lower and upper canyon compared with the more realistic LES-chemistry model. This suggests that the segregation effect due to incomplete mixing reduces the chemical conversion rate of NO to NO2. This study reveals the impacts of nonlinear O3-NOx-VOC photochemical processes in the incomplete mixing environment and provides a better understanding of the pre-processing of emissions within canyons, prior to their release to the urban boundary layer, through the coupling of street canyon dynamics and chemistry.",
keywords = "Nonlinear photochemistry, Large eddy simulation, Street canyon, Segregation effect",
author = "Jian Zhong and Xiaoming Cai and William Bloss",
year = "2017",
month = feb,
day = "12",
doi = "10.1016/j.envpol.2017.01.076",
language = "English",
journal = "Environmental Pollution",
issn = "0269-7491",
publisher = "Elsevier",

}

RIS

TY - JOUR

T1 - Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry

AU - Zhong, Jian

AU - Cai, Xiaoming

AU - Bloss, William

PY - 2017/2/12

Y1 - 2017/2/12

N2 - A large eddy simulation (LES) model coupled with O3-NOx-VOC chemistry is implemented to simulate the coupling effect of emissions, mixing and chemical pre-processing within an idealised deep (aspect ratio = 2) urban street canyon under a weak wind condition. Reactive pollutants exhibit significant spatial variations in the presence of two vertically aligned unsteady vortices formed in the canyon. Comparison of the LES results from two chemical schemes (simple NOx-O3 chemistry and a more comprehensive Reduced Chemical Scheme (RCS) chemical mechanism) shows that the concentrations of NO2 and Ox inside the street canyon are enhanced by approximately 30-40% via OH/HO2 chemistry. NO, NOx, O3, OH and HO2 are chemically consumed, while NO2 and Ox (total oxidant) are chemically produced within the canyon environment. The within-canyon pre-processing would increase oxidant fluxes released from the canyon to the overlying boundary layer, and this effect is more crucial for deeper street canyons (as found in many traditional European urban centres) than shallower (lower aspect ratio) streets. There is clear evidence of distinct behaviours for emitted chemical species and entrained chemical species, and positive (or negative) values of intensities of segregations are found between pairs of species with a similar (or opposite) behaviour. The simplified two-box model underestimated NO and O3 levels, but overestimated NO2 levels for both the lower and upper canyon compared with the more realistic LES-chemistry model. This suggests that the segregation effect due to incomplete mixing reduces the chemical conversion rate of NO to NO2. This study reveals the impacts of nonlinear O3-NOx-VOC photochemical processes in the incomplete mixing environment and provides a better understanding of the pre-processing of emissions within canyons, prior to their release to the urban boundary layer, through the coupling of street canyon dynamics and chemistry.

AB - A large eddy simulation (LES) model coupled with O3-NOx-VOC chemistry is implemented to simulate the coupling effect of emissions, mixing and chemical pre-processing within an idealised deep (aspect ratio = 2) urban street canyon under a weak wind condition. Reactive pollutants exhibit significant spatial variations in the presence of two vertically aligned unsteady vortices formed in the canyon. Comparison of the LES results from two chemical schemes (simple NOx-O3 chemistry and a more comprehensive Reduced Chemical Scheme (RCS) chemical mechanism) shows that the concentrations of NO2 and Ox inside the street canyon are enhanced by approximately 30-40% via OH/HO2 chemistry. NO, NOx, O3, OH and HO2 are chemically consumed, while NO2 and Ox (total oxidant) are chemically produced within the canyon environment. The within-canyon pre-processing would increase oxidant fluxes released from the canyon to the overlying boundary layer, and this effect is more crucial for deeper street canyons (as found in many traditional European urban centres) than shallower (lower aspect ratio) streets. There is clear evidence of distinct behaviours for emitted chemical species and entrained chemical species, and positive (or negative) values of intensities of segregations are found between pairs of species with a similar (or opposite) behaviour. The simplified two-box model underestimated NO and O3 levels, but overestimated NO2 levels for both the lower and upper canyon compared with the more realistic LES-chemistry model. This suggests that the segregation effect due to incomplete mixing reduces the chemical conversion rate of NO to NO2. This study reveals the impacts of nonlinear O3-NOx-VOC photochemical processes in the incomplete mixing environment and provides a better understanding of the pre-processing of emissions within canyons, prior to their release to the urban boundary layer, through the coupling of street canyon dynamics and chemistry.

KW - Nonlinear photochemistry

KW - Large eddy simulation

KW - Street canyon

KW - Segregation effect

U2 - 10.1016/j.envpol.2017.01.076

DO - 10.1016/j.envpol.2017.01.076

M3 - Article

JO - Environmental Pollution

JF - Environmental Pollution

SN - 0269-7491

ER -