Trends in atmospheric elemental carbon concentrations from 1835 to 2005

Elemental carbon (EC) aerosols absorb solar radiation which results in heating of the atmosphere. Recent increases in the atmospheric burden of EC may account for similar to 10 to 15% of global warming. Long-term EC data, however, are sparse. We report here our measurements of annual mean atmospheric EC concentration, [EC](atm), from filter samples collected daily from 1978 to 2005 at Whiteface Mountain, NY using the thermal optical method. The [EC](atm) for 1978-1986, 1987-1996, and 1997-2005 were, 550, 225, and 62 ng m(-3), respectively. We also collected similar to 55 cm long sediment cores from West Pine Pond near Whiteface Mountain. The cores were sliced and their Pb-210 ages determined. The first (top) five slices each represented sediment deposition over 7 years and the remaining 13 years each. EC was chemically separated from the sediment samples from four cores, and its concentration in each slice was determined using the thermal optical method. The [EC] sed followed closely that of [EC](atm) from 1978 to 2005. Assuming wet and dry deposition as the only source, we can show that [EC](sed) = K[EC](atm), where K ( m(3) g(-1)) is a constant for a given lake. From [EC](atm), and [EC](sed) for the 1978-2005 period, K was determined to be 10,400 +/- 4,400 m 3 g(-1). With this value used for K and [EC](sed), the [EC](atm) values were determined from 1835 to 1978. The [EC](atm) from 1835-1862 was similar to 30 ng m(-3), which may be close to the preindustrial background level. The [EC](atm) was 65 ng m(-3) for the 1863-1875 period, then increased sharply, reaching a maximum value, 760 ng m(-3), from 1917-1930. From 1931-1943 through 1978-1984, the concentration decreased gradually, from 680 to 560 ng m(-3). The concentrations for 1985-1991, 1992-1998, and 1999-2005 were 295, 195, and 60 ng m(-3), respectively. Model calculations for BC emissions from fossil fuel combustion for the US by Novakov et al. (2003) qualitatively reproduce the trend determined experimentally in this work.