In 1969 the North Atlantic Treaty Organization (NATO) established the Committee on Challenges of Modern Society (CCMS). The subject of air pollution was from the start one of the priority problems under study within the framework of various pilot studies undertaken by this Committee. The organization of a yearly conference dealing with air pollution modeling and its application has become one of the main activities within the pilot study relating to air pollution. The international conference was organized for the first five years by the United States and for the second five years by the Federal Republic of Germany. Belgium, represented by the Prime Minister's Office for Science policy, became responsible in 1980 for organizing the third five years of the annual conference. This volume contains the papers presented at the 15th NATO/CCMS International Technical Meeting (ITM) on Air Pollution Modeling and Its Application, held in St. Louis, Missouri, from the 15th to 19th April 1985. This ITM was jointly organized by the Prime Minister's Office for Science Policy, Belgium (Pilot Country); by the Environmental Protection Agency, Atmospheric Sciences Research Laboratory, United States (Host Country); and by Washington University, Mechanical Engineering Department (Host Organization).