Showing papers by "Rex Britter published in 2010"

Global Mortality Attributable to Aircraft Cruise Emissions

Abstract: Aircraft emissions impact human health though degradation of air quality. The majority of previous analyses of air quality impacts from aviation have considered only landing and takeoff emissions. We show that aircraft cruise emissions impact human health over a hemispheric scale and provide the first estimate of premature mortalities attributable to aircraft emissions globally. We estimate ∼8000 premature mortalities per year are attributable to aircraft cruise emissions. This represents ∼80% of the total impact of aviation (where the total includes the effects of landing and takeoff emissions), and ∼1% of air quality-related premature mortalities from all sources. However, we note that the impact of landing and takeoff emissions is likely to be under-resolved. Secondary H2SO4−HNO3−NH3 aerosols are found to dominate mortality impacts. Due to the altitude and region of the atmosphere at which aircraft emissions are deposited, the extent of transboundary air pollution is particularly strong. For example, w...

Large-Eddy Simulation of Flow and Pollutant Transport in Urban Street Canyons with Ground Heating

Abstract: Our study employed large-eddy simulation (LES) based on a one-equation subgrid-scale model to investigate the flow field and pollutant dispersion characteristics inside urban street canyons. Unstable thermal stratification was produced by heating the ground of the street canyon. Using the Boussinesq approximation, thermal buoyancy forces were taken into account in both the Navier-Stokes equations and the transport equation for subgrid-scale turbulent kinetic energy (TKE). The LESs were validated against experimental data obtained in wind-tunnel studies before the model was applied to study the detailed tur- bulence, temperature, and pollutant dispersion characteristics in the street canyon of aspect ratio 1. The effects of different Richardson numbers (Ri) were investigated. The ground heat- ing significantly enhanced mean flow, turbulence, and pollutant flux inside the street canyon, but weakened the shear at the roof level. The mean flow was observed to be no longer isolated

Construction of Digital Elevation Models for a Southern European City and a Comparative Morphological Analysis with Respect to Northern European and North American Cities

Abstract: A morphometric analysis of a southern European city and the derivation of relevant fluid dynamical parameters for use in urban flow and dispersion models are explained in this paper. Calculated parameters are compared with building statistics that have already been computed for parts of three northern European and two North American cities. The aim of this comparison is to identify similarities and differences between several building configurations and city types, such as building packing density, compact versus sprawling neighborhoods, regular versus irregular street orientation, etc. A novel aspect of this work is the derivation and use of digital elevation models (DEMs) for parts of a southern European city. Another novel aspect is the DEMs’ construction methodology, which is low cost, low tech, and of simple implementation. Several building morphological parameters are calculated from the urban DEMs using image processing techniques. The correctness and robustness of these techniques have be...

Coupling Mesoscale Modelling with a Simple Urban Model: The Lisbon Case Study

Abstract: The ongoing trend of urbanisation worldwide is leading to a growing requirement for detailed flow and transport parameterisations to be included within numerical weather prediction (NWP) models. Such models often employ a simple roughness parameterisation for urban areas, which is not particularly accurate in predicting or assessing the flow and dispersion at street scale. Moreover, this kind of parameterisation offers too poor a representation of the mechanical and thermal forcing exerted by urban areas on the larger scale flow. At present, high computational costs and long simulation running times are among the constraints for the implementation of more detailed urban sub-models within NWP models. To overcome such limitations, a downscaling procedure from the atmospheric flow at the synoptic scale to the neighbourhood scale and below, is presented in this study. This is achieved by means of a simple urban model based on a parameterised formulation of the drag exerted by the building on the airflow. Application of the urban model for estimating spatially-averaged mean wind speed and the urban heat island over a selected neighbourhood area in Lisbon, Portugal, is presented. The results show the capability of the urban model to provide more accurate mean wind and temperature profiles. Moreover, the urban model has the advantage of being cost effective, as it requires small computational resources, and thus is suitable to be adopted in an operational context. The model is simple enough to be also used to assess how the resolving of urban surface processes may affect those at the larger scales.

Construction of Digital Elevation Models for a Southern European City and a Comparative Morphological Analysis with Respect to Northern European and North American Cities

Abstract: A morphometric analysis of a southern European city and the derivation of relevant fluid dynamical parameters for use in urban flow and dispersion models are explained in this paper. Calculated parameters are compared with building statistics that have already been computed for parts of three northern European and two North American cities. The aim of this comparison is to identify similarities and differences between several building configurations and city types, such as building packing density, compact versus sprawling neighborhoods, regular versus irregular street orientation, etc. A novel aspect of this work is the derivation and use of digital elevation models (DEMs) for parts of a southern European city. Another novel aspect is the DEMs’ construction methodology, which is low cost, low tech, and of simple implementation. Several building morphological parameters are calculated from the urban DEMs using image processing techniques. The correctness and robustness of these techniques have be...

Prediction of street canyon velocities

Abstract: We created an empirical model using analytical formulas to predict the bulk veloc- ities in street canyons and the shear stress on rough urban surfaces based on atmospheric veloci- ty, average size and distribution of obstructions characteristic of building surfaces, and canyon orientation. The model is based on control volume arguments, entrainment and exchange pro- cesses, connections between the Nikuradse sand grain roughness and both the skin friction coef- ficient and the form of complex urban surfaces, and correlations for the urban canyon problem found using CFD in a generic form. This work can be applied at a neighborhood scale both ana- lytically, using spatially averaged neighborhood parameters, and in simulation, using a shear stress boundary condition to approximate rough urban surfaces.