Air dispersion model- ing is widely used to estimate the concen- tration of ground- level pollutants from emission sources. Dispersion models often are utilized dur- ing preparation and evaluation of air permit applications, and in other instances where air pollution control strategies must be evaluated or improved. One commonly used model is SCREEN3, which offers a simple, easy-to-use method of ob- taining pollutant concentration estimates. About This Article This article is the second in a two-part series on air dispersion modeling. In the spring 2003 issue of this journal, two authors of this article presented an introduction to air dispersion modeling (Cora & Hung, 2003). In a theoretical and practical discussion intended to help environmental compliance personnel un- derstand the basis of air pollution dispersion modeling, we presented basic concepts and sum- marized some findings from our review of the professional literature available on the topic. In this article, we present practical information on using one particular dispersion model- ing tool: SCREEN3, which is used dur- ing permitting eval- uation procedures. We include a hypothetical case study demonstrat- ing the use of SCREEN3 for determining the maxi- mum allowable ground level concentration (MAGLC) of air toxics released at an industrial emission source. We also explain the basic con- cepts associated with the use of SCREEN3. Development of the SCREEN3 Model The SCREEN3 model was developed to provide a simple method for obtaining pollutant concen- tration estimates based on screening procedures. The current model was preceded by two earlier versions (SCREEN and SCREEN 2.0). The program originally was developed in a DOS version, which Environmental Quality Management / Summer 2003 / 67 © 2003 Wiley Periodicals, Inc. Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/tqem.10087 Mario G. Cora, Yung-Tse Hung, and Doritza Pagan-Rodriguez Air Dispersion Modeling: Using SCREEN3 to Determine the MAGLC of Air Toxics Second of a two-part series