Air Quality Research Center News
Chris Cappa Studies Arctic Haze Aboard the Research Vessel Knorr
Posted on: January 12, 2009
Chris Cappa, professor of environmental engineering at UC Davis, took part in a 39-day research cruise to the Arctic aboard the research vessel Knorr in March and April, 2008. The goal of the ICEALOT, the International Chemistry Experiment in the Arctic LOwer Troposphere, was the characterization of aerosol and gas pollution levels in the Arctic marine boundary layer atmosphere in a region near the edge of the sea-ice, with a particular focus on short-lived pollutants.
Recent years have seen a significant decline in the abundance of Arctic sea-ice. Besides the influence of greenhouse gases, particles in the atmosphere that absorb solar radiation (e.g. soot) can have a strong warming effect on the climate. Soot plays an additional role in the Arctic through deposition on white snow and ice, effectively decreasing the reflectivity of the snow and ice -this leads to greater light absorption at the surface and increased melting of the ice. As sea-ice melts, darker ocean water is exposed to direct sunlight causing the region to absorb even more solar radiation and to warm even faster. This is called a positive feedback and usually referred to as the ice-albedo feedback.
Cappa went in the springtime because, he explains, "there exists an 'Arctic Haze' that develops every spring, and we hoped to extensively study the composition of this haze in an effort to determine the primary source of the haze." An important component of this haze is soot, which can deposit to the sea-ice at a time just after the winter sea-ice maximum, setting up conditions for melting that will continue throughout the spring and summer months.
Cappa was directly involved in making measurements of light absorption and light scattering by atmospheric aerosols. Light absorption measurements give an indirect measurement of atmospheric soot levels since soot is the primary light absorbing component of atmospheric aerosol. As such, the results will provide new insights into the levels of soot that exist in the atmosphere above the sea-ice and that can (and probably will) eventually deposit to the ice surface. Preliminary analysis confirms that soot is a small but important component of the Arctic Haze. Their measurements will provide new constraints for climate models in terms of how well they can simulate pollution levels in the Arctic.
"We started the cruise in Woods Hole, MA where we spent a few days looking at air quality along the East Coast, in particular in the Long Island Sound," Cappa says. "We then made a long journey across the North Atlantic ocean. Not a pleasant journey in the springtime. Eventually we crossed the Arctic Circle and then spent a week or so sampling local air pollution sources near the northern parts of Europe. After a one-day stop in Tromso, Norway, we headed north, eventually making it as far as 80 degrees N. We then moved down through the Arctic Ocean following along the edge of the sea-ice as close as was safe before finally ending the cruise in Reykjavik, Iceland."
The cruise was funded by NOAA.
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