Airshed dispersion models

The Portland airshed dispersion model GRID (7.) is a conservation of mass, advectlon-diffusion code designed to perform... 

The development of new source apportionment methods have, for the first time, led to the development of regional particulate control strategies. Source impacts assigned using a chemical mass balance (CMB) model have been used in association with airshed dispersion models to identify emission inventory deficiencies and Improve modeling assumptions. 

Urban aerosols are complicated systems composed of material from many different sources. Achieving cost-effective air particle reductions in airsheds not meeting national ambient air quality standards requires identification of major aerosol sources and quantitative determination of their contribution to particle concentrations. Quantitative source Impact assesment, however, requires either calculation of a source s impact from fundamental meteorological principles using source oriented dispersion models, or resolving source contributions with receptor models based on the measurement of characteristic chemical and physical aerosol features. Q)... 

Experience gained during the past four years has shown that data base improvement programs such as those implemented in Oregon have provided new perspectives into the nature of each airshed s emissions. Subsequent major changes in each community s emission Inventories have Improved dispersion modeling results and provided a level of dispersion model verification Impossible to attain using traditional hl-vol measurements alone. 

Air quality control r ions (aqcr s), 128 Air quality prediction models, 195, 678-79 airshed photodiemical, 218 balance-equation, 205 box, 213-15, 219 classification of, 200-205 criteria for selecting, 219-20 deterministic, 203 dispersion, 205 explanation of, 1% for episode control, 202 for land-use planning, 201-2 for physiochemical transformations, 208-10... 

Several types of models are commonly used to describe the dispersion of atmospheric contaminants. Among these are the box, plume, and puff models. None are suitable, however, for describing the coupled transport and reaction phenomena that characterize atmospheres in which chemical reaction processes are important. Simulation models that have been proposed for the prediction of concentrations of photochemically formed pollutants in an urban airshed are reviewed here. The development of a generalized kinetic mechanism for photochemical smog suitable for inclusion in an urban airshed model, the treatment of emissions from automobiles, aircraft, power plants, and distributed sources, and the treatment of temporal and spatial variations of primary meteorological parameters are also discussed. 

T Trban airshed models are mathematical representations of atmospheric transport, dispersion, and chemical reaction processes which when combined with a source emissions model and inventory and pertinent meteorological data may be used to predict pollutant concentrations at any point in the airshed. Models capable of accurate prediction will be important aids in urban and regional planning. These models will be used for ... 

Atmospheric transport and dispersion processes are expressed in an airshed model in numerous way. Wind speed and direction enter through the component variables, u, v, and to (or more generally u x,y,z,t)). The... 

The above described results illustrate the strengths and weaknesses of the two box models. The Eulcrian box model is easy to apply but oversimplifies everything by assuming a homogeneous airshed. The Lagrangian model can provide more information, such as, for example, a spatial distribution of concentrations, but by neglecting horizontal dispersion, it may predict higher concentrations downwind of emission sources. 

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