A comparison of data from the atmospheric research stations at Summit, Greenland, and Zeppelin, Svalbard
Researchers from the U.S. and Norway have recently started an informal collaboration to share resources used to interpret atmospheric chemistry data and exploit data together from the Summit, Greenland and Zeppelin, Svalbard stations (Sjostedt et al., 2006; Stohl et al., 2006). SUMSVAL shall strengthen this collaboration between the research communities.
The two stations have contrasting characteristics: Zeppelin, at rather low elevation, is in the direct outflow of pollution from Eurasia and sees frequent episodes of so-called Arctic Haze. Summit, in contrast, is located at high altitude and sees little influence from Arctic Haze but is well positioned to sample the Arctic free troposphere. Summit is also influenced frequently by biomass burning pollution plumes from North America, which are less pronounced at Zeppelin. A comparison of the data from these two stations, therefore, is likely to enhance our general understanding of air pollution in the Arctic and its effects on Arctic climate. This project shall build closer links between Norwegian and U.S. researchers by conducting joint data interpretation, developing transport climatologies, and coordinating research activities. Extended (about 1 month every year) visits of NILU researchers in the U.S., and invited travel of U.S. researchers to NILU and Svalbard are foreseen.
Major objectives of this project are to
· Strengthen the relationships between U.S. and Norwegian researchers working with atmospheric chemistry data from Summit and Zeppelin.
· Harmonize IPY activities of the project partners.
· Engage actively in the interpretation of measurement data from Summit.
· Build a comparative transport climatology for Summit and Zeppelin to identify differences in source regions of air pollution for the two stations.
· Do comparative analyses of key chemical measurements (e.g., ozone, black carbon, carbon monoxide) performed at both stations.
There are several important open questions regarding pollution input into the Arctic and its influence on Arctic climate. Arctic Haze, first described by Greenaway (1950), was traditionally believed to originate mostly from sources in high-latitude Eurasia (Barrie, 1986; Stohl, 2006). However, recently Koch and Hansen (2005) have suggested that most of the black carbon in the Arctic atmosphere originates in southern Asia, as a result of rapidly growing emissions there. In contrast, Stohl (2006) suggested that biomass burning in the boreal region is the largest black carbon source in the summer and perhaps even in total for the Arctic, whereas Asian black carbon contributes significantly only at high altitudes of the atmosphere. Since black carbon is important for the radiative forcing (Hansen and Nazarenko, 2004) of the Earth-atmosphere system, both through absorption of radiation in the atmosphere as well as through its impact on the albedo of ice surfaces, it is urgent to clarify where Arctic black carbon is coming from. The Arctic is particularly important for this because of the highly reflective ice/snow surfaces, which enhance the black carbon effects in the atmosphere and are also susceptible to influence from black carbon deposition. This can best be achieved by comparing data from different stations with very different characteristics (location relative to main pollutant pathways, altitude). This approach was successfully used recently by Stohl et al. (2006) to show that black carbon can be enhanced throughout the Arctic as a result of boreal forest fires.
A comparison of Zeppelin and Summit data will likely allow clarifying some of these questions. While Zeppelin is ideally located in the pathway of anthropogenic pollution from Eurasia, Summit is influenced directly by forest fire pollution plumes. Comparing the data from these two stations and for different seasons will allow identifying the different sources of air pollution in the Arctic. Because of its high altitude and cold environment, Summit is also an ideal location for exploring black carbon deposition on the snow and its effect on the albedo.
In preparation of the forthcoming International Polar Year (IPY) and the IPY core project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport), which is coordinated by the applicant of this proposal, resources for the interpretation of transport processes were recently made available for both the Summit station and the Zeppelin station. These resources are meant to help researchers working at both stations interpret their chemical data. For this purpose, the Lagrangian particle dispersion model FLEXPART (Stohl et al., 2005) was run in backward mode every three hours for a period of several years. An example for one of the model products is shown in Fig. 1. It shows the emission sensitivity for the first phase of the most extreme pollution episode ever recorded at the Zeppelin station (highest ozone concentrations, highest BC and particle concentrations, largest aerosol optical depth observations, etc.), which occurred in April/May of this year. Folding the emission sensitivity with conventional emission inventories showed that there was indeed a pronounced contribution of pollution from fossil fuel combustion in Europe that, however, was not higher than during “normal” Arctic Haze episodes. Superimposed on the emission sensitivity map are fire hot spots detected by the MODIS satellite that are spatially and temporally co-located with high emission sensitivity on a daily basis (there were some fires also further east, which are not shown). Most of the fires occurred on agricultural land and released tremendous amounts of particles and trace gases. Fig. 1 shows that the smoke clouds originating from these fires traveled to Svalbard within about 3 days (numbers in Fig. 1 correspond to transport times in days), which is confirmed by satellite imagery. Conditions during the first days of May were even more extreme, with yet higher pollution records set and also led to a dark coloration of the snow on Svalbard (John Burkhart, personal communication). Similar analyses were also made by Stohl et al. (2006) for both Summit and Zeppelin, for an episode of strong burning in the boreal forest of North America, which influenced both stations, and also other Arctic stations (Barrow, Alaska and Alert, Canada).
As part of POLARCAT, it has been proposed to extend the web-based model products back in time, make them a near-real-time service, and also produce them for other Arctic stations. In the meantime, however, although the websites are on-line since only a few months, they have become quite popular and have already led to the submission of two joint publications of researchers from the U.S. and Norway (Sjostedt et al., 2006; Stohl et al., 2006). We, therefore, suggest here to extend this collaboration to also include a comparative data analysis from both stations to address some of the questions posed above (and also some others).
Figure 1. Footprint emission sensitivity for an air mass arriving at Zeppelin station on 27 April 2006 between 18 and 21 UTC. Red dots indicate satellite-detected fires on forested land, black dots are fires on agricultual land.
We suggest the following activities to be done as part of this proposal:
Interpretation of Summit data. The U.S. partners have all signalled interest in using our transport model data to interpret their measurement data or have already used them. We suggest engaging actively in the interpretation of these data, for instance by also providing specialized model products, producing plots of publication quality, discussion of the results, interpretation, etc.
Comparative transport climatologies for Zeppelin and Summit. We suggest using the transport model results for at least a 10-year period for building comparative climatologies of transport for both Zeppelin and Summit. The pathways of pollution from various source regions (boreal forest region; high-latitude Eurasia, eastern and southern Asia, North America) shall be compared for the two stations. Particular emphasis shall be put on differences in altitude by doing transport calculations also for a virtual station at the altitude of Summit but the location of Zeppelin.
Comparative data interpretation. We propose to analyze the concentrations of key chemical species and aerosols (e.g., ozone, black carbon, carbon monoxide, etc.) for which long-term measurements from both sites are available. The seasonality, mean values and extremes shall be compared for the two stations to learn about the relative importance of different source for the two stations. Extreme episodes such as the one described by Stohl et al. (2006) that affect both stations shall also be studied to characterize the spatial extent of pollution phenomena.
We suggest to do part of our research abroad, i.e., spend time at the partner institutes, and also invite U.S. researchers to visit NILU and Svalbard. This project will, thus, also serve to harmonize major IPY activities in both countries.
Barrie, L. A, 1986. Arctic air-pollution – an overview of current knowledge, Atmos. Environ., 20, 643-663.
Greenaway, K. R., 1950. Experiences with Arctic flying weather, Royal Meteorological Society Canadian Branch (Nov. 30, 1950), Toronto, Ontario, Canada.
Hansen, J., and L. Nazarenko, 2004. Soot climate forcing via snow and ice albedos, Proc. Natl. Acad. Sci., 101, 423-428.
Koch, D., and J. Hansen, 2005. Distant origins of Arctic black carbon: A Goddard Institute for Space Studies model experiment. J. Geophys. Res., 110, D04204, doi:10.1029/2004JD005296.
S. J. Sjostedt, L. G. Huey, D. J. Tanner, J. Pieschl, G. Chen, J. E. Dibb, B. Lefer, M. A. Hutterli, A. J. Beyersdorf, N. J. Blake, D. R. Blake, D. Sueper, T. Ryerson, J. Burkhart, and A. Stohl (2006): Observations of hydroxyl and the sum of peroxy radicals at Summit, Greenland during the 2003 summer field study. Submitted to Atmos. Environ.
Stohl, A. (2006): Characteristics of atmospheric transport into the Arctic troposphere. J. Geophys. Res. 111, D11306, doi:10.1029/2005JD006888.
Stohl, A., C. Forster, A. Frank, P. Seibert, and G. Wotawa (2005): Technical Note : The Lagrangian particle dispersion model FLEXPART version 6.2. Atmos. Chem. Phys. 5, 2461-2474.
Stohl, A., E. Andrews, J. F. Burkhart, C. Forster, D. Kowal, C. Lunder, T. Mefford, J. A. Ogren, S. Sharma, N. Spichtinger, K. Stebel, R. Stone, J. Ström, K. Tørseth, and C. Wehrli (2006): Pan-Arctic enhancements of light absorbing aerosol concentrations due to North American boreal forest fires during summer 2004. Submitted to J. Geophys. Res. Available also from http://zardoz.nilu.no/~andreas/publications/blackcarbon.pdf