Showing papers by "Rex Britter published in 2003"
TL;DR: In this article, the authors address flow and dispersion in urban areas at four scales: regional, city, neighborhood, and street, and address the most appropriate framework to study and quantify the result.
Abstract: ▪ Abstract Increasing urbanization and concern about sustainability and quality of life issues have produced considerable interest in flow and dispersion in urban areas. We address this subject at four scales: regional, city, neighborhood, and street. The flow is one over and through a complex array of structures. Most of the local fluid mechanical processes are understood; how these combine and what is the most appropriate framework to study and quantify the result is less clear. Extensive and structured experimental databases have been compiled recently in several laboratories. A number of major field experiments in urban areas have been completed very recently and more are planned. These have aided understanding as well as model development and evaluation.
798 citations
TL;DR: In this paper, a spatially averaged model is derived for UC, the characteristic in-canopy velocity, and the model's predictions are compared with experimental results from various sources.
140 citations
TL;DR: In this article, the dispersion mechanisms of a passive tracer in a two-dimensional model of a street canyon were investigated experimentally and analytically, demonstrating the importance of external turbulence properties on the transfer.
107 citations
TL;DR: In this article, a simple baseline urban dispersion model is suggested for use in simulating near-surface releases of tracer chemicals in the urban canopy layer, accounting for low wind speeds, nearly neutral stabilities, large turbulence intensities, and large initial mixing in urban areas.
84 citations
TL;DR: In this paper, the authors address the problem of parameterization of traffic induced turbulent motion in urban dispersion models and propose a new dispersive velocity scale to account for traffic induced air motions in predictions of street-canyon pollution levels.
Abstract: The paper addresses the problem of the parameterisation of traffic induced turbulent motion in urban dispersion models. Results from a variety of full-scale and wind-tunnel studies are analysed and interpreted within a modelling framework based on scaling considerations. The combined effects of traffic and wind induced dispersive motions are quantified for different traffic situations (variable traffic densities, vehicle velocities and vehicle types) and incorporated into the developed parameterisations. A new dispersive velocity scale is formulated and recommendations regarding its application in urban dispersion models are given. The necessity of accounting for traffic induced air motions in predictions of street-canyon pollution levels is demonstrated. Further research is needed to verify the empirical constants in the proposed parameterisations and to generalize the developed approach for a broader range of urban building configurations, meteorological conditions, and traffic situations.
77 citations
TL;DR: In this article, a theoretical framework to estimate mechanical turbulence induced by traffic in street canyons at low wind speed conditions is established, where the standard deviation of the velocity fluctuations is adopted as a measure of traffic-produced turbulence.
Abstract: The modelling of pollutant dispersion at the street scale in an urban environment requires the knowledge of turbulence generated by the traffic motion in streets. In this paper, a theoretical framework to estimate mechanical turbulence induced by traffic in street canyons at low wind speed conditions is established. The standard deviation of the velocity fluctuations is adopted as a measure of traffic-produced turbulence (TPT). Based on the balance between turbulent kinetic energy production and dissipation, three different parameterisations for TPT suitable for different traffic flow conditions are derived and discussed. These formulae rely on the calculations of constants that need to be estimated on the basis of experimental data. One such estimate has been made with the help of a wind tunnel data set corresponding to intermediate traffic densities, which is the most common regime, with interacting vehicle wakes.
67 citations
TL;DR: In this paper, the short-range vertical dispersion of a passive containment in a neutrally stratified turbulent boundary layer can be usefully characterised by a number of approaches, such as a vertical diffusivity, Kz, a vertical Gaussian dispersion parameter, σz, and an entrainment velocity, we.
25 citations
16 Sep 2003
8 citations
16 Sep 2003
TL;DR: In this paper, urban air pollution involves physical and chemical processes over a wide range of space and time scales, and these processes influence the larger regional scale up to 100 or 200 km by providing a momentum sink and a thermal and pollutant source.
Abstract: Urban air pollution involves physical and chemical processes over a wide range of space and time scales. Cities have typical spatial scales up to 10 to 20 km, or possibly even larger when several adjacent urban areas coalesce to form a conurbation. Pollutant dispersion from near-ground level sources would be present through much of the atmospheric boundary layer over these distances. Processes at the city scale influence the larger regional scale up to 100 or 200 km by providing a momentum sink and a thermal and pollutant source. At the same time the regional, or larger, scale physical processes provide the background state for the city scale processes. Ozone episodes occur over the entire city or larger conurbation and, as they occur under particular meteorological conditions, may occur over a much larger region.
3 citations