Welcome to the homepage of the Atmospheric Physics and Composition Modelling Group. We are part of Atmospheric Physics in the Department of Physics at the University of Toronto. Our research uses newly available satellite measurements of atmospheric trace gases together with global three-dimensional modelling of tropospheric chemistry and transport to develop a better understanding of how pollution influences the dynamical and chemical state of the lower atmosphere. The recent satellite observations are, for the first time, providing a global view of the atmospheric distribution of a broad range of environmentally important trace gases. We are using these data to better characterize the pathways for long-range transport of pollution, to quantify the impact of this pollution on the atmospheric environment, and to obtain an improved understanding of the year-to-year variability of these transport pathways and their dependence on the mean state of the climate system.