This dissertation applies a global chemical transport model (GEOS-Chem) together with ground-based, aircraft, and satellite observations to quantify the sources, transport pathways, and chemical processing of tropospheric pollution in the Arctic.

Asian anthropogenic emissions are shown to be the dominant source of carbon monoxide (CO) pollution throughout the Arctic troposphere, except near the surface where European anthropogenic emissions are similarly important. Despite anomalously large fires in spring 2008, biomass burning is found to contribute little to mean CO during that period. AIRS satellite data are used to demonstrate a link between El Niño and Asian pollution transport to the Arctic, with transport hindered in 2008 due to a weakened Aleutian Low associated with La Niña conditions.

Sulfate-ammonium aerosol in the Arctic is found to derive from a more complicated mix of sources. European and East Asian emissions are important but not dominant sources of sulfate. Anthropogenic emissions from West Asia (Russia and Kazakhstan) are shown to provide the largest source of sulfate to the Arctic lower troposphere in winter. Ammonium is mostly from European and East Asian sources. In spring 2008, a large contribution from boreal fires resulted in a more neutralized aerosol in the free troposphere than at the surface. Aerosol transported to the Arctic from East Asia and Europe is found to be mostly neutralized, while West Asian and North American aerosol is highly acidic. Recent growth of sulfur emissions in West Asia may explain observations of increasing aerosol acidity in Alaska over the past decade.

Mercury in the Arctic shows a different seasonality from other pollutants, with a spring minimum driven by bromine chemistry over sea ice followed by a summer maximum. GEOS-Chem simulations of surface observations are used to argue that the summer peak cannot be explained by atmospheric transport, re-emission from snowpacks, or ocean kinetics. Instead, Russian rivers are proposed to provide a large flux of mercury to the Arctic Ocean in spring-summer, with subsequent evasion to the atmosphere driving the observed summer peak. The Arctic Ocean then provides a net source to the atmosphere, with rivers the dominant mercury source to the Arctic environment.