Eastern Asia has a large number of megacities including many regions of ongoing rapid urbanization with the potential to produce new megacities in the coming decades. Recent field experiments and associated modeling studies in eastern China, Korea and Japan have demonstrated that human activities in Eastern Asia megacities have had dramatic impacts on atmospheric chemistry and physics in this region which have important implications for air quality and climate. These studies are characterizing emission and ambient distributions, atmospheric chemical processing, aerosol and oxidant production and growth, urban/rural interactions, and long range transport. It is widely recognized that individual megacities can influence other regions and effective air pollution control strategies in any of these locations requires a better understanding of emissions, chemical processing and interactions within the entire region. This special issue will highlight recent field studies and associated modeling investigations that address scientific questions associated with the impact of Eastern Asia megacities on atmospheric chemistry and physics. Papers submitted to this special issue will focus on Eastern Asia megacity studies of chemical emission and deposition, atmospheric chemical composition and processing, impacts on weather and climate, regional transport and related topics. This will include investigations conducted within specific megacities of Korea, Japan and Eastern China as well as larger scale studies linking individual Eastern Asia megacities to the regional and global environment.