Variability of Midlatitude Transport and Mixing In a Warmer World

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Air quality over the western United States is determined not only by local emissions, but also by the transport of pollutants from outside the region, namely, from Asian emissions that have been transported across the Pacific Ocean, and by stratospheric intrusion events that bring naturally-occurring ozone-rich air to the surface. Quantifying the contribution of the large-scale atmospheric transport to present-day air quality is of vital importance for policy makers, since the ability of an area to be in compliance with current air quality standards is partly a function of the background meteorological conditions. Furthermore, increasing greenhouse gas concentrations over the next century are expected to drive large changes in the midlatitude circulation, but the effects of these changes on pollutant transport are not well understood.The goals of this project are (1) to gain a fundamental understanding of the dynamical mechanisms that couple synoptic variability and pollutant transport and (2) to explore how changes in synoptic variability with increased greenhouse gas concentrations may modify this transport. The two goals will be addressed using a hierarchy of models: a large-multi-model data set, a chemistry-climate model, a stratosphere-resolving atmospheric GCM and an idealized, dry dynamical core. Future pollutant emissions are largely unpredictable, but the dynamical processes that drive tropospheric transport have the potential to be understood. By decoupling emissions from the circulation, this work aims to assess the role of changing atmospheric variability in modifying tropospheric transport.