Street canyon atmospheric composition: coupling dynamics and chemistry

Bright, Vivien Bianca (2013). Street canyon atmospheric composition: coupling dynamics and chemistry. University of Birmingham. Ph.D.

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A new model for the simulation of street canyon atmospheric chemical processing has been developed, by integrating an existing Large-Eddy Simulation (LES) dynamical model of canyon atmospheric motion with a detailed chemical reaction mechanism, the Reduced Chemical Scheme (RCS), comprising 51 chemical species and 136 reactions, based upon a subset of the Master Chemical Mechanism (MCM).

The combined LES-RCS model is used to investigate both the effects of mixing and chemical processing upon air quality within an idealised street canyon. The effect of the combination of dynamical (segregation) and chemical effects is determined by comparing the outputs of the full LES-RCS canyon model with those obtained when representing the canyon as a zero-dimensional box model (i.e. assuming mixing is complete and instantaneous).

The LES-RCS approach predicts lower (canyon-averaged) levels of NOX, OH and HO2, but higher levels of O3, compared with the box model run under identical chemical and emission conditions. Chemical processing of emissions within the canyon leads to a significant increase in the Ox flux from the canyon into the overlying boundary layer, relative to primary emissions, for the idealised case and a number of pollution scenarios considered. These results demonstrate that within-canyon atmospheric chemical processing can substantially alter the concentrations of pollutants injected into the urban canopy layer, compared with the raw emission rates within the street canyon and that such variations have a considerable effect on average within canyon concentrations and the flux of pollutants out of the canyon into the urban background environment.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
College/Faculty: Colleges (2008 onwards) > College of Life & Environmental Sciences
School or Department: School of Geography, Earth and Environmental Sciences
Funders: None/not applicable
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > Q Science (General)
T Technology > TD Environmental technology. Sanitary engineering


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