Meteorology of the Local Scale

Each of these scales of atmospheric motion plays a role in air pollution, although over different periods of time. For example, the microscale meteorological effects determine the dispersion of a plume from an industrial stack or a highway over timescales on the order of minutes to a few hours. On the other hand, mesoscale phenomena take place over hours or days and influence the transport and dispersal of pollutants to areas that are hundreds of kilometers from their sources. 

Atmospheric Chemistry and Physics From Air Pollution to Climate Change, Second Edition, by John H. Seinfeld and Spyros N. Pandis. Copyright 2006 John Wiley Sons, Inc. 

FIGURE 16.1 Measured daily average PM2.5 concentrations during 2001-02 in an urban area (Pittsburgh, PA). 

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The use of local theories, incorporating parameters such as the eddy viscosity Km and eddy thermal conductivity Ke, has given reasonable descriptions of numerous important flow phenomena, notably large scale atmospheric circulations with small variations in topography and slowly varying surface temperatures. The main reason for this success is that the system dynamics are dominated primarily by inertial effects. In these circumstances it is not necessary that the model precisely describe the role of turbulent momentum and heat transport. By comparison, problems concerned with urban meso-meteorology will be much more sensitive to the assumed mode of the turbulent transport mechanism. The main features of interest for mesoscale calculations involve abrupt... 

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