A new PACES-coordinated modeling/measurement project focused on reducing errors in model descriptions of pollutant transport, wet removal, and chemistry at mid- and high-latitudes is being developed. This project, IMPAACT (Investigation of Multiscale Processes Affecting Atmospheric Chemical Transport) will examine the transport and evolution of aerosol and gas-phase pollutants originating in East Asia and exported to the Arctic and North America. IMPAACT will use a semi-Lagrangian approach to track these pollutants throughout lifting to the free troposphere, transport across the North Pacific, and arrival to the polar regions and the western U.S. and Canada. The role of wet removal and aqueous processes will be foci of this study, as model simulations suggest particular sensitivity of the nitrogen/ozone and aerosol budgets to these processes. IMPAACT observations will be anchored by the NASA DC-8 aircraft, which has the payload, range, and altitude capability needed for trans-Pacific measurements. Additional aircraft will operate at lower altitudes near East Asia, Alaska, western Canada, and the Northwest of the contiguous U.S. Mountaintop, surface, and shipborne observations will provide valuable information on the spatial and temporal variability of pollutant characteristics and transport. Modeling efforts will include Lagrangian, regional, global chemical transport, and chemistry-climate models, to be used for sensitivity studies, prognostic runs, and comparisons with observations. Satellite observations will be assimilated in some model runs and will provide essential data for subsequent analyses. It is anticipated that the intensive airborne portion of IMPAACT will take place in spring 2021, with flights based out of southern Japan/Okinawa, Alaska, and western North America. A U.S. scientific steering committee has written a white paper; international collaboration is solicited to further develop the science plans and execute the study.