This document is Volume II of a three-volume revision of Air Quality Criteria for Particulate Matter and Air Quality Criteria for Sulfur Oxides, first published in 1969 and 1970, respectively. By law, air quality criteria documents are the basis for establishment of the National Ambient Air Quality Standards (NAAQS). The Air Quality Criteria document of which this volume is a part has been prepared in response to specific requirements of Section 108 of the Clean Air Act, as amended in 1977. The Clean Air Act requires that the Administrator periodically review, and as appropriate, update and reissue criteria for NAAQS. To assist the reader in putting the effects into perspective with the real-world environment, Chapters 2 through 7 in the present volume (Volume II) have been prepared. The chapters of Volume II discuss essential points regarding: physical and chemical properties; air monitoring and analytical measurement techniques; sources and emissions; transport, transformation, and fate; and observed ambient concentrations of the pollutants. Also, Chapter 7 in this volume introduces the reader to the contemporary problem of acidic deposition and potential contributions of sulfur oxides to acidic deposition phenomena.