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Export efficiency of black carbon aerosol in continental outflow: Global implications
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honululu, Hawaii, USA
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
National Center for Atmospheric Research, Boulder, Colorado, USA
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
National Center for Atmospheric Research, Boulder, Colorado, USA
Department of Chemistry, Drexel University, Philadelphia, Pennsylvania, USA
Department of Chemistry, Drexel University, Philadelphia, Pennsylvania, USA
NASA Langley Research Center, Hampton, Virginia, USA
Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
We use aircraft observations of Asian outflow from the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) mission over the NW Pacific in March–April 2001 to estimate the export efficiency of black carbon (BC) aerosol during lifting to the free troposphere, as limited by scavenging from the wet processes (warm conveyor belts and convection) associated with this lifting. Our estimate is based on the enhancement ratio of BC relative to CO in Asian outflow observed at different altitudes and is normalized to the enhancement ratio observed in boundary layer outflow (0–1 km). We similarly estimate export efficiencies of sulfur oxides (SO x = SO2(g) + fine SO4 2−) and total inorganic nitrate (HNO3 T = HNO3(g) + fine NO3 −) for comparison to BC. Normalized export efficiencies for BC are 0.63–0.74 at 2–4 km altitude and 0.27–0.38 at 4–6 km. Values at 2–4 km altitude are higher than for SO x (0.48–0.66) and HNO3 T (0.29–0.62), implying that BC is scavenged in wet updrafts but not as efficiently as sulfate or nitrate. Simulation of the TRACE-P period with a global three-dimensional model (GEOS-CHEM) indicates that a model timescale of 1 ± 1 days for conversion of fresh hydrophobic to hydrophilic BC provides a successful fit to the export efficiencies observed in TRACE-P. The resulting mean atmospheric lifetime of BC is 5.8 ± 1.8 days, the global burden is 0.11 ± 0.03 Tg C, and the decrease in Arctic snow albedo due to BC deposition is 3.1 ± 2.5%.
Received 11 September 2004; accepted 10 March 2005; published 1 June 2005.
Citation: (2005), Export efficiency of black carbon aerosol in continental outflow: Global implications, J. Geophys. Res., 110, D11205, doi:10.1029/2004JD005432.
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