Minimizing the effect of automotive pollution in urban geometry using mathematical optimization

One of the factors that needs to be considered during the layout of new urb an geometry (e.g. street direction, spacing and width, building height rest rictions) is the effect of the air pollution associated with the automotive transport that would use routes in this urban area. Although the pollution is generated at street level, its effect can be widespread due to interact ion of the pollutant dispersion and diffusion with the wind speed and direc tion. In order to study the effect of a new urban geometry on the pollutant levels and dispersion. a very time-consuming experimental or parametric nu merical study would have to be performed. This paper proposes an alternativ e approach, that of combining mathematical optimization with the techniques of computational fluid dynamics (CFD). In essence, the meteorological info rmation as represented by a wind rose (wind speed and direction), is used t o calculate pollutant levels as a function of urban geometry variables: str eet canyon depth and street canyon width. The pollutant source specified in conjunction with a traffic scenario with CO is used as pollutant. The main aim of the study is to be able to suggest the most beneficial configuratio n of an idealized urban geometry that minimizes the peak pollutant levels d ue to assumed traffic distributions. This study uses two mathematical optim ization methods. The first method is implemented through a successive maxim ization-minimization approach, while the second method determines the locat ion of saddle points of the pollutant level, considered as a function of ur ban geometry and wind rose. Locally, a saddle point gives the best urban ge ometry for the worst meteorological scenario. The commercial CFD code, STAR -CD, is coupled with a version of the DYNAMIC-Q optimization algorithm of S nyman, first to successively locate maxima and minima in a min-max approach : and then to locate saddle points. It is shown that the saddle-point metho d is more cost-effective. The methodology presented in this paper can readi ly be extended to optimize traffic patterns for existing geometry or in the development of geometry modification for pollution control or toxic releas es. (C) 2000 Elsevier Science Ltd. All rights reserved.