Polar Regions, with their extensive ice cover, are naturally sensitive to changes in surface air temperatures, and therefore could provide evidence of global temperature changes due to anthropogenic emissions. The melting of ice sheets as a result of global warming will have catastrophic effects on human beings, primarily due to sea level rise, and potential impacts on ocean and atmospheric circulation. Extensive experiments were planned in spring and summer of 2008 to coincide with and in support of the International Polar Year (IPY; 2007-2009)), and include investigations affiliated with the POLARCAT (POLar study using Aircraft, Remote sensing, surface measurements and modelling of Climate, chemistry, Aerosols and Transport). The NASA effort, known as the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS), provide opportunities to study the Arctic atmosphere and surface properties and processes from ground-, airborne-, and satellite-based measurements in an integrated manner. Satellite measurements have provided global views of the Earth, which show significant decreases in sea ice cover, providing evidence that climate change is proceeding fastest at the high latitudes of the Arctic and Antarctic.

ARCTAS focuses on advancing understanding of the factors driving current changes in the Arctic region including transport of mid-latitude pollution, boreal forest fires, aerosol radiative forcing, and chemical processes. During the winter and spring, pollutants from the mid-latitudes are transported to the Arctic, contributing to the occurrence of Arctic haze. During the spring and summer, biomass burning emissions are transported to the Arctic as a result of boreal forest fires and agricultural burning. Industrial, urban, and shipping activities and natural emissions within the Arctic also provide sources for gases and aerosols. These species alter the chemistry of the Arctic atmosphere, radiative forcing within the atmosphere and at the surface, and surface albedo and reflectance. The current climate models do not properly account for the regional radiative forcing from aerosols and tropospheric ozone, which may play a particularly large role in the Arctic radiative budget and climate response. Also, observation of the Arctic from space poses unique challenges including bright and cold surfaces, low sun angles, seasonal darkness, and extensive cloud cover. In addition, many species of environmental interest are not directly observable from space. ARCTAS aimed to use detailed observations from aircraft to provide the validation, retrieval constraints, correlative data, and process information needed to better achieve the potential of satellites for Arctic research. The plan is for the combination of satellite and aircraft data to provide together powerful information for constraining and evaluating models of Arctic atmospheric composition and climate, and thus improve model projections of future change.

ARCTAS involved three NASA aircraft: a DC-8 with detailed chemical payload, a P-3B with detailed aerosol payload, and a B-200 with remote aerosol instrumentation. April flights sampled pollution plumes from all three mid-latitude continents, fire plumes from Siberia and Southeast Asia, and halogen radical events. June-July flights focused on boreal forest fire influences and sampled fresh fire plumes from northern Saskatchewan as well as older fire plumes from Canada, Siberia, and California. The summer ARCTAS deployment was preceded by one week of DC-8 and P-3B flights over and around California to address state issues of air quality and climate forcing. These flights were sponsored by the California Air Resources Board (CARB). Activities were therefore conceived to try to focus attention on Polar Regions in support of the IPY.

The CAR flew aboard P-3B aircraft and obtained imagery of clouds and various Earth surface features in the Arctic and measured spectral and angular distribution of scattered light by aerosols, clouds, snow, sea ice, and melt ponds under a variety of conditions in order to determine bidirectional reflectance distribution function (BRDF), and hence albedo, of sea ice (with snow and snow-free), water ponds (from melted sea ice), and clouds, and to determine aerosol optical properties over various surfaces for satellite validation. The CAR was funded by NASA's Radiation Sciences Program (Dr. Hal Maring).