Urban Dispersion Model

In another review, Hoffert discussed the social motivations for modeling air quality for predictive purposes and elucidated the components of a model. Meteorologic factors were summarized in terms of windfields and atmospheric stability as they are traditionally represented mathematically. The species-balance equation was discussed, and several solutions of the equation for constant-diffusion coefficient and concentrated sources were suggested. Gaussian plume and puff results were related to the problems of developing multiple-source urban-dispersion models. Numerical solutions and box models were then considered. The review concluded with a brief outline of the atmospheric chemical effects that influence the concentration of pollutants by transformation. 

Hanna, S. R. Diurnal Variation of the Stability Factor in the Simple ATDL Urban Dispersion Model. J. Air Pollut. Contr. Assog. 28 147-150 (1978). 

Important issue for urban dispersion modelling is the characteristics of the release, e.g., radiochemical composition, density for gases, size distribution for aerosols, etc. For radioactive aerosols the particle size distribution (e.g., number of modes, distribution type, average diameter and standard deviation for each mode, density, and nuclides) varies significantly for different release types and from one nuclide to another. The particle size spectrum could be very broad, e.g. 0.001-200 fim. 

The possibility of a release in an urban environment signifies the importance of having fast robust urban dispersion models available. Comprehensive models involving e.g. CFD and LES are probably not feasible in real time. Due to the influence of the urban environment on the meteorology, it is important to make use of urban-scale numerical weather prediction model data. 

Therefore, for emergency forecasting in the local-scale of urban areas very simplified dispersion models with simply urbanised meteo-preprocessors are still used (see, e.g., overview by Hanna et al., 2004 [259] Britter and Hanna, 2003 [81] Britter, 1998 [79]). A brief overview of such urban dispersion models is given below ... 

UDM (Urban Dispersion Model) (Hall et al., 2002 [248]) is a widely-used model developed by the UK Defence Science and Technology Laboratory (DSTL) based on assumptions of a Gaussian shape and empirical parameterizations developed from special field and laboratory experiments involving obstacle arrays. 

The verification of the above mentioned six urban dispersion models versus the Salt Lake City Urban 2000 field data (Allwine et al., 2002 [7]) is analysed by Hanna et al., 2004 [259] and presented in Figure 9.18. The points represent maximum hourly-averaged C/Q for each of 18 trials and 7 monitoring arcs. 

Hall, D.J., Spanton, A.M., Griffiths, I.H., Hargrave, M., and Walker, S. (2002) The Urban Dispersion Model (UDM) Version 2.2 Technical Documentation. DSTL/TR04774, Porton Down, Salisbury SP40JQ UK. 

Hanna, S.R., Britter, R., and Franzese, P. (2003) A baseline urban dispersion model evaluated with Salt Lake City and Los Angeles tracer data, Atmos. Environ 37, 5069-5082. 

Hanna, S., Fabian, P., Chang, J., Venkatram, A., Britter, R., Neophytou, M Brook, D. (2004) Use of urban 2000 field data to determine whether there are significant differences between the performance measures of several urban dispersion models, AMS-2004 Annual Meeting, paper 7.3. 

Ketzel, M., Louka, P, Sahm, R, Guilloteau, E., Sini, J.F., and Moussiopoulos, N. (2002) Intercomparison of Numerical Urban Dispersion models - Part II. Street Canyon in Hannover, Germany. Water, Air, and Soil Pollution, Focus 2, 603-613. 

Schatzmann, M., and Leitl, B. (2002) Validation and application of obstacle resolving urban dispersion models, Atmospheric Environment 36, 4811-4821. 

Hanna, S. R., and Chang, J. C., Modification of the Hybrid Plume Dispersion Model (HPDM) for urban conditions and its evaluation using the Indianapolis data set. Report... 

Gaussian dispersion model computations were made for all "urbanized areas" (248) for each of the 77 area source categories, for a total of 19,096 runs. 

Modelling of levels and atmospheric transport of drugs of abuse in the urban environment results from ambient levels of dmgs of abuse within the city could be introduced in dispersion models for simulate atmospheric transport of these substances in urban environments. This methodology can be combined with health population data and other tools such as GIS-based systems in order to generate health-risk maps. 

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)... 

Kumar P, Ketzel M, Vardoulakis S, Pirjola L, Britter R (2011) Dynamics and dispersion modelling of nanoparticles from road traffic in the urban atmospheric environment -a review. J Aerosol Sci 42 580-603... 

Certainly a number of aspects are not covered by this overview, such as ultrafine particle or secondary organic aerosol formation processes and their roles on air quality degradation, urban-scale dispersion models for air quality modelling or the... 

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. 

Multiple Source Urban Atmospheric Dispersion Model, Argonne National Laboratory, Argonne (1970). 

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