William (Bill) Randel is a Senior Scientist in the Atmospheric Chemistry Observations and Modeling (ACOM) Laboratory at NCAR, and head of the Chemical Climate Section in ACOM. Bill received his PhD in Physics from Iowa State University. He came to NCAR as an Advanced Study Program Postdoctoral Fellow, followed by a staff Scientist position, and was Director of Atmospheric Chemistry Division during 2007-2015. Bill’s research focuses on analysis of observational data related to the large-scale circulation, constituent transport and long-term changes in the atmosphere, using global satellite measurements and model simulations. He has been a contributing and lead author for the UNEP/WMO Scientific Assessments of Ozone Depletion and IPCC Climate Assessment Reports, and has served on numerous committees and panels related to atmospheric composition and climate.