Historical Trends in Atmospheric Elemental Carbon Concentrations Across Northeastern US, 1850-2005

Light-absorbing elemental carbon (EC) aerosol plays a key role in the earth's temperature regulation because of its strong ability to absorb solar radiation, and may be the second biggest contributor to global warming after greenhouse gases, accounting for ~15 to 30 ‰ of global warming estimates. Long-term EC data, however, are sparse. The primary objective of this study is to determine atmospheric elemental (EC) or black carbon concentrations for the ~1850 2005 period in the northeastern US. The data will be used to validate the models that have been used to predict atmospheric EC burden based on various types and quantity of fuels used and estimated emissions taking into consideration the technology used. We report here (1) direct measurements of EC in filters at Whiteface Mountain (44.37^{0}N, 73.90^{0}W), NY, from 1978 through 2005, and (2) determine atmospheric concentrations from measurements in lake sediments going back to ~1850. We have collected aerosols on Whatman 41 filters at this site every 24 or 48 h continuously from July 1978 to present, with few lapses. Monthly composites were made from the daily samples, cellulose removed by treating the filters with 70‰ sol of ZnCl2 at 50^{0}C, and EC transferred onto a quartz filter. The monthly EC concentrations were determined using the thermal-optical method. The EC concentrations at Whiteface Mountain showed a stepwise decreasing trend. The mean EC concentrations for the 1978-86, 1987- 96, and 1997-2005 periods were, 0.540, 0.221, and 0.065μg m-3, respectively. No robust seasonal effects in EC concentrations were observed. We also collected sediment cores from two lakes, Clear Pond (43.99^{0}N, 73.82^{0}W), and West Pine Pond (44.34^{0}, 74.43^{0}W) near Whiteface Mountain and within the same air-shed. The cores were sliced to represent estimated accumulation of five to 10 years. The sediment samples were weighed, freeze dried to constant weight, and the ages of individual sections determined using the 210Pb dating method. Each sediment section was subjected to a previously tested chemical method and EC separated, purified and deposited on a quartz filter. The EC concentrations were determined using the same thermal-optical method as for the filters. The EC record in the lake sediments mimics the EC profile observed for the aerosols for the period the data is available, 1978-2005. Known major features such as the great Adirondack forest fires in 1903, and 1908 are visible in the EC recode. The data will be compared with the most recent emission inventory. This work was partially funded by the US National Science Foundation.