Page 337 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

Chapter 11
Air Dispersion

For the air pollutants penetrating though the post-combustion air pollution control
devices, dispersion is the last step to minimize the environmental impact. An air
dispersion models can be employed for predicting concentrations downwind of the
source for environmental impact assessments, risk analysis, emergency planning,
and development and implementation of air emission standards.
A great amount of models have been developed and they can be categorized into
four generic classes:

• Gaussian models
• Numerical models
• Statistical models
• Physical models
Many air dispersion models are available at the US EPA websites for free use. In
general, the more complex models are more reliable. In this chapter, we only
introduce three kinds of models with different levels of complexity. Advanced
models for special applications can be found in the book by de Visscher [21].
This chapter starts with an introduction to some basic concepts that are critical to
the understanding of different air dispersion models. Then basic models will be
introduced. All of the models introduced herein are based on conservation of mass
(or material balances) in a control volume. Most models can be used for predicting
the concentrations of several different pollutants, but they must be applied sepa-
rately to one pollutant at a time. At the end, comments on advanced models will be
given, although they are not discussed in a great depth.

11.1 Box Model

A box model is the simplest one for air dispersion in a ground-level community. It
is useful in such well-defined environments as tunnels, streets with high rise
buildings, community in a valley, and indoor environments. It is assumed that air in

© Springer Science+Business Media Singapore 2014 315
Z. Tan, Air Pollution and Greenhouse Gases, Green Energy and Technology,
DOI 10.1007/978-981-287-212-8_11