Trace Gases in the Arctic Atmosphere

Abstract

The Arctic atmosphere is coupled to lower latitudes, both as a receptor for global pollution and as a driver for the global climate system. Arctic atmospheric composition is variable and changing, making measurements of trace gas concentrations essential for understanding atmospheric processes. The atmospheric concentrations of carbon dioxide (CO2) and methane in the Arctic are increasing in concert with global trends. Meanwhile, the Arctic represents up to 25% of the global land carbon sink and the Arctic Ocean accounts for 10–12% of the global ocean CO2 sink. The Arctic thus has a strong influence on the global carbon cycle, while also responding more strongly to changes in climate than do mid-latitude regions. However, many processes that lead to carbon emissions and exchange in the Arctic are poorly understood and the region is sparsely sampled, resulting in large uncertainties in the quantification of carbon stocks, sources, and sinks. The Arctic experiences poor air quality due to local sources and transport from diverse mid-latitude emission sources such as wildfires. The springtime Arctic troposphere frequently experiences ozone depletion episodes that are linked to surface-based production of reactive halogen species that then deplete ozone, particularly associated with bromine explosions. A major source of bromine in the Arctic is sea salt, but the importance of blowing snow and the mechanisms involved in the heterogeneous bromine release are the focus of ongoing research. In the stratosphere, springtime ozone depletion continues in the Arctic, with significant interannual variability driven by atmospheric dynamics, transport, and temperature. Ozone recovery is anticipated due to reduction of chlorofluorocarbons under the Montreal Protocol and its Amendments, but there are uncertainties due to coupling between stratospheric chemistry and climate. This chapter provides a review of the trace gas composition of the Arctic atmosphere. It surveys our current knowledge and discusses outstanding questions, with a focus on tropospheric ozone and halogens, greenhouse gases, and the stratosphere.