Collection and Analysis of GEOSummit Aerosols

Fine particles directly scatter and absorb sunlight, and depending on their size and composition can either heat or cool the Earth. They come from both natural sources like volcanoes, dust storms, and forest fires, and from man-made sources like industry, power plants and vehicles. Since a signature of their origin is imbedded in their composition, they can be tracked back to sources even thousands of miles away using meteorological models. Understanding the composition and sources of these fine particles is critical to developing better models of global climate change, but requires many years of observation. One of the best places to measure these fine particles in the atmosphere is at the Greenland Summit research station because the site is not near populated areas or the ocean which are sources of these particles. This renewal of an Arctic Observing Network project will extend sampling of these fine particles at the Greenland Summit site another 5 years. The results will be of value to global climate modelers and to atmospheric scientists. Undergraduate students will be involved in sample analysis. This program is unique in that the Greenland Summit site is the only high elevation Arctic site and thus responds to aerosols in the free troposphere, the region of the atmosphere that dominates long range transport. Since 2003, aerosols have been collected continuously in 8 size modes, 15 µm to 0.09 µm, on slowly rotating drums that allow for 12 hr. time resolution and an excellent match to the various transport patterns that bring aerosols into the Arctic. Since there is very little mass to analyze, the large synchrotron x-ray source at the Lawrence Berkeley Laboratory Advanced Light Source has been used to make the compositional analyses, yielding the lowest values of many aerosol species ever measured in the ambient atmosphere. The new program has several enhancements. Optical back scattering will allow measurement of the global albedo, which is important since aerosols are roughly responsible for 2/3 of the total uncertainty in global climate models. A new method has been added for measuring aerosol organic matter that will allow mass closure. In this protocol, the sum of all species equals the total mass present in each of the 8 size modes so that all aerosol mass can be accounted for in determination of the optical properties. The higher energy beams at the Stanford Synchrotron Radiation Light Source will now also be included, allowing the program to access heavier elements to better identify industrial sources. These data will be compared with other high elevation sites like the Mauna Loa Observatory in Hawaii to better track long-range transport of aerosols in the Northern hemisphere. A further benefit of these data is that they allow a measurement of how airborne particles get imbedded in the snow pack and eventually the ice cores collected at the Summit site. Thus, these measurements help explain the dust present over the past millennia, during both warm periods and ice ages.