Lagrangian Modeling of Plume Dispersal in the Urban Boundary LayerEPA Grant Number: R828178
Title: Lagrangian Modeling of Plume Dispersal in the Urban Boundary Layer
Investigators: Weil, Jeffrey C.
Institution: University of Colorado at Boulder , Cooperative Institute for Research in Environmental Sciences
EPA Project Officer: Shapiro, Paul
Project Period: September 1, 2000 through August 31, 2002
Project Amount: $172,773
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Engineering and Environmental Chemistry
Existing dispersion models for point sources in urban areas are deficient due to an inadequate treatment of the turbulence structure above cities. The structure is modified by the larger urban roughness elements and the different surface thermal properties relative to rural areas. These modifications lead to a shallow well-mixed urban boundary layer (UBL) at night, within which the turbulence can be strong. As a result, plumes from short- or moderately tall stacks disperse more rapidly and can produce high ground-level concentrations (GLCs).
The aim of the proposed research is to improve our knowledge and predictive capability of buoyant plume dispersion in the urban environment with focus on the nocturnal case. There are three key objectives. The first is to increase our understanding of the depth and structure of the nocturnal UBL through both modeling studies and model comparisons with observations. The second objective is to further develop a hybrid Lagrangian dispersion model for predicting pollutant concentrations in buoyant plumes. This approach couples a stochastic model for the plume meander with an entrainment model for the plume rise and growth. The hybrid model will be extended to the urban environment and will include a new "lofting" model for plumes trapped within the nocturnal UBL. The third objective is to improve an analytical PDF model and extend its range of applicability by coupling it with the UBL description and the new lofting model. The extended hybrid and PDF models will be compared with appropriate field data and modified as necessary.
It is expected that this effort will enhance the realism and range of conditions over which these dispersion models provide credible estimates of concentrations. The focus is on the situation---lofting in the nocturnal UBL---that leads to high GLCs for elevated sources in cities. The investigation will provide basic understanding necessary for dealing with and estimating the peak concentration of toxic and hazardous substances as well as criteria pollutants; these estimates are needed in risk assessments.