Oslo: POLARCAT continues hunt for data with follow-up project

The POLARCAT programme has a neat acronym but a convoluted full name – its official long title is "Polar study using aircraft, remote sensing, surface measurements and models of Climate, chemistry, Aerosols and Transport".

Measurements of the atmosphere from aircraft are essential in the Arctic as the reflective nature of the ice surface makes it difficult for satellites to detect atmospheric concentrations of chemicals correctly. The POLARCAT project combined research aircraft with ground-based campaigns, including the use of a train on the trans-Siberian railway. The results should help to verify satellite measurements.

One key finding has been that the impact of biomass burning on Arctic aerosol levels is even larger than expected, POLARCAT co-ordinator Andreas Stohl of the Norwegian Institute for Air Research told environmentalresearchweb at the IPY Oslo Science Conference.

The phenomenon of Arctic haze was discovered by pilots in the 1950s but remained unexplained until the 1970s, when scientists detected sulphate particles at ground level. They ascribed both these and the higher-level aerosols to pollution that had travelled up from mid-latitudes from sources such as fossil fuel combustion and Russian smelters.

However, Stohl believes that the higher-level haze has been misclassified; POLARCAT results indicates that the haze aloft is soot formed as a result of biomass burning rather than anthropogenic sulphate emissions. Such burning can have natural causes (e.g. forest fires) or it can be a result of man's activities like agricultural burning. "The magnitude of the biomass burning was surprising," said Stohl; more than half of the aerosols aloft were from biomass burning.

Some scientists believe that black carbon (soot) emissions from Eurasia may have contributed as much as carbon dioxide to earlier snowmelt but there is much still to learn in this area.

Models of atmospheric transport are not currently doing a good job at high latitudes, according to Stohl. In the Arctic pollution plumes are typically stretched horizontally and vertically, he explained. This makes life tricky for models, which tend to struggle with fine filaments. The new observational data collected during POLARCAT will help researchers to check and develop the models. But new information is also needed – for example, how precipitation scavenges particles.

With that in mind, the CLIMSLIP (Climate impacts of short-lived pollutants in the polar regions) project will continue some of POLARCAT's work. CLIMSLIP, which will involve six or seven countries, had a kick-off meeting last Monday. As part of the programme, Finnish researchers will create known amounts of black carbon by burning, and measure how the particles deposit onto ice in both dry and wet conditions. This will provide information about how snowfall rates affect scavenging. Other participants will measure albedo (surface reflectivity) and snowmelt; the first experiment is due to begin next year.

CLIMSLIP will also fund the analysis of some of the only aerosol data measured from aircraft in Antarctica. Taken by a German team in 2006 and 2007, the data have yet to be examined.