Atmospheric physical and chemical processes span a wide range of scales, from a few meters to thousands of kilometers at the planetary scale. Advances in observational and modeling capabilities, as well as enhanced computing resources, have enabled multi-scale investigations of atmospheric processes that are influenced by both large-scale forcing and small-scale heterogeneities, such as complex terrain and the urban environment. This session seeks contributions that explore high-resolution simulations, multi-scale techniques and observational campaigns aiming to investigate weather, climate, energy, wildfires and air quality issues at the kilometer and sub-kilometer scale. We particularly encourage real case studies seeking to investigate the capability and significance of kilometer and sub-kilometer scale simulations, as well as idealized studies to improve understanding and predictability of physical and chemical processes in the boundary layer across scales. Results from observational campaigns with dense instrumentation to measure kilometer-scale variability are also welcomed.