Presenting the quantum mechanical theory of pressure broadening and its application in atmospheric science, this is a unique treatment of the topic and a useful resource for researchers and professionals alike. Rayer proceeds from molecular processes to broad scale atmospheric physics to bring together both sides of the problem of remote sensing. Explanations of the relationship between a series of increasingly general theoretical papers are provided and all key expressions are fully derived to provide a firm understanding of assumptions made as the subject evolved. This book will help the atmospheric physicist to cross into the quantum world and appreciate the more theoretical aspects of line shape and its importance to their own work.