The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will support a twenty-four-month research fellowship by Dr. Susan D. Kaspari to work with Dr. Margit Schwikowski at Paul Scherrer Institute in Villigen, Switzerland.
Carbonaceous particles (CP) can significantly contribute to global warming; yet CP remain one of the largest sources of uncertainty in analyses of climate change during the industrial era. Due to the existence of only a few historical records of CP, studies assessing the role of CP in climate change used estimated inventories of CP concentrations based on wood and/or fossil fuel consumption data. However, many important CP sources such as residential emissions from cooking and heating are very difficult to estimate in the present, even more difficult to estimate for the past, and can vary greatly through time and with location. Thus, more quantitative measurements of CP emissions and atmospheric concentrations as a function of time are needed to estimate climate change related to CP forcing. This project will produce records of carbonaceous particle (CP) concentrations spanning pre-industrial to modern time from previously collected ice cores from three sites in the Himalayas and Tibetan Plateau. Ice cores from mountain glaciers provide high-resolution archives of past atmospheric and environmental conditions, and preserve information about natural and anthropogenic atmospheric composition, and aerosol and contaminant transport and deposition. The ice cores are from sites that are strategically located to provide a history of CP emissions from Eurasia. CP deposition histories from this region are key to understanding the climatic impacts of CP, as the atmospheric composition in this region is heavily influenced by the largest sources of CP globally. The applicant and host will analyze the ice cores at high-resolution for black carbon (BC) via an optical method, and elemental carbon (EC) and organic carbon (OC) via a thermal method, and use the records to investigate the role of CP in regional and global climate change since pre-industrialization. To date Schwikowski and colleagues at PSI have produced the only historical ice core CP records spanning pre-industrial to modern times.
This project provided research support through the International Research Fellowship Program for me to work with Margit Schwikowski, in the Analytical Chemistry Group at the Paul Scherrer Institut (PSI) in Switzerland. The primary objective of this research was to reconstruct black carbon (BC) concentrations in the atmosphere using ice cores from the Himalaya and Tibetan Plateau. At the time I was awarded the fellowship, Dr. Schwikowski and colleagues had produced the only historical ice core record of carbonaceous particles spanning pre-industrial to modern times. BC produced by the incomplete combustion of biomass, coal and diesel fuels can significantly contribute to climate change by altering the Earth’s radiative balance. BC in the atmosphere absorbs light and causes atmospheric heating, whereas BC deposited on snow and glaciers can darken the surface, resulting in greater energy absorption and melt [Flanner et al., 2009; Hansen and Nazarenko, 2004; Ramanathan and Carmichael, 2008]. Historical records of BC concentration and distribution in the atmosphere are needed to determine the role of BC in climate change, however most studies have relied on estimated inventories based on wood and/or fossil fuel consumption data [Bond et al., 2007]. Reconstructing BC concentrations in Asia is particularly important because this region has some of the largest BC sources globally, which negatively impact climate, water resources, agriculture and human health [Auffhammer et al., 2006; Chameides et al., 1999; Menon et al., 2002]. Interest in BC in the Himalayas has recently increased due to concerns that BC is contributing to glacier retreat via atmospheric heating and BC deposition on glacier surfaces. During my International Research Fellowship at PSI, I gained experience analyzing ice cores for BC using two methods: 1) A thermal-optical method, which has been widely used in atmospheric applications, but that is problematic for analyzing Asian ice cores for BC because high dust concentrations cause complications. 2) The Single Particle Soot Photometer (SP2). PSI was the second laboratory globally to apply the SP2 to measuring BC in liquid samples. Advantages of this method over the thermal-optical method is that relatively small sample volumes are required, thus ice cores can be analyzed at high temporal resolution, yielding information about BC seasonality. Further, this method in general is not affected by the presence of other light absorbing impurities such as dust. The laboratory training I received at PSI was instrumental to my early career development. I left Switzerland to begin an assistant professor position, and received NSF funding to acquire an SP2 instrument in my laboratory to continue with the research I initiated in Switzerland. In addition to method development work, two main studies resulted from my fellowship research: Recent increase in black carbon concentrations from a Mt. Everest ice core spanning 1860-2000 AD [Kaspari et al., 2011]. The SP2 ice core BC record demonstrates strong seasonality, with peak concentrations during the winter?spring, and low concentrations during the summer monsoon season. BC concentrations from 1975–2000 relative to 1860–1975 have increased approximately threefold, indicating that BC from anthropogenic sources is being transported to high elevation regions of the Himalaya. The timing of the increase in BC is consistent with BC emission inventory data from South Asia and the Middle East, however since 1990 the ice core BC record does not indicate continually increasing BC concentrations. The Everest BC and dust records provide information about absorbing impurities that can contribute to glacier melt by reducing the albedo of snow and ice. Spatial and seasonal variations in black carbon concentrations in snow and ice in the Solu-Khumbu, Nepal [Kaspari et al., in prep.]. Snow and ice samples were collected from crevasse profiles and snowpits at elevations between 5400 and 6400 m asl from Mera glacier located in the Solu-Khumbu region of Nepal on the southern slope of the Himalaya during spring and fall 2009, and measured using the SP2. BC concentrations peak during the winter-spring, and are substantially higher at elevations < 6000 m than > 6000 m due to post-depositional processes and/or greater loading in the lower troposphere. BC concentrations in the winter-spring snow/ice horizons are sufficient to reduce albedo and potentially hasten snow and ice melt, however lower BC concentrations from summer monsoonal snowfall that coincides with the peak ablation season likely reduces the efficacy of BC to accelerate summer melt. Because the largest areal extent of snow and ice resides at elevations < 6000 m, the higher BC concentrations at these elevations can reduce the snow and glacier albedo over large areas, potentially accelerating melt, affecting glacier mass-balance and water resources, and contributing to a positive climate forcing. Further observational studies are needed to assess the contribution of BC relative to other absorbing impurities to albedo reductions and snow and ice melt.
