Since early 2020, the COVID-19 pandemic has resulted in a series of restrictions in mobility and economic activity, in countries around the world, designed to prevent the spread of the virus. These have caused sudden and prolonged change in emissions, especially from the transportation sector, which have provided a unique opportunity to examine how air pollution and greenhouse gases respond to such a perturbation. This session will focus on what we have learned from these sudden changes about air pollution and greenhouse gas sources. We encourage submissions on the effect of emission changes on levels of trace gas and particulate compounds and what we can learn from this about future air pollution and carbon emission issues. The session will examine methodologies for assessing the effect of restrictions on emissions and concentrations and we encourage the submission of local, regional and global studies incorporating in situ, remote sensing or modelling data.