Dr. Daewon Byun (1955- 2011) established a high standard of science, service and stewardship in a career that spanned academia, the private sector, and government service. His research in atmospheric science, begun in graduate studies at North Carolina State University in the 1980's, was inspired by his previous education and military service as a weather officer in Korea. After earning his Ph. D. in 1987, he worked in the private sector (ERT and CSC) as scientific programmer and modeler for atmospheric simulations related to dispersion and air quality. He then joined NOAA's Atmospheric Modeling Division in the Air Resources Laboratory (1992) in Research Triangle Park, assigned to EPA's National Exposure Research Laboratory, to develop and test advanced models used in regulatory applications for air quality. Among his many activities, he tested and implemented the Regional Acid Deposition Model, and designed and developed the Community Multi-scale Air Quality (CMAQ) modeling system for EPA's regulatory applications. Dr. Byun's approach supported the integration of a reactive chemical transport model, driven by emissions inputs and a meteorological model focused on the dynamics and physics of the planetary boundary layer and free troposphere. This work garnered much recognition, including both NOAA and EPA award medals, and led to his involvement in many collaborations and committees in the US and internationally. When he was offered the opportunity to join the University of Houston's Department of Geosciences (2001), he moved rapidly to start a new program in atmospheric sciences, and participated as a lead scientist in the modeling activities associated with the Texas Air Quality field campaign of 2006. He re-joined NOAA's ARL in 2008, this time in Silver Spring, Maryland, to lead a group devoted to atmospheric chemistry modeling, with responsibility for improvements to NOAA/NWS's National Air Quality Forecast capability. Throughout these many transitions, Dr. Byun strengthened his ever-expanding network of collaborations, enriching the diverse communities and disciplines that are integrated in air quality modeling. Dr. Byun's scholarship, leadership and vision have left a lasting legacy in the Nation's air quality modeling and prediction capabilities and will remain a cornerstone for our future efforts in these fields. We celebrate his contributions with papers inspired by his work in this memorial session.