absorption
; aerosol
; airborne survey
; altitude
; atmospheric convection
; biomass burning
; black carbon
; brown carbon
; climate forcing
; radiation balance
; radiative forcing
; radiative transfer
; spatiotemporal analysis
; top of atmosphere
; tropopause
; troposphere
; vertical distribution
; United States
英文摘要:
Carbonaceous aerosols affect the global radiative balance by absorbing and scattering radiation, which leads to warming or cooling of the atmosphere, respectively. Black carbon is the main light-absorbing component. A portion of the organic aerosol known as brown carbon also absorbs light. The climate sensitivity to absorbing aerosols rapidly increases with altitude, but brown carbon measurements are limited in the upper troposphere. Here we present aircraft observations of vertical aerosol distributions over the continental United States in May and June 2012 to show that light-absorbing brown carbon is prevalent in the troposphere, and absorbs more short-wavelength radiation than black carbon at altitudes between 5 and 12 km. We find that brown carbon is transported to these altitudes by deep convection, and that in-cloud heterogeneous processing may produce brown carbon. Radiative transfer calculations suggest that brown carbon accounts for about 24% of combined black and brown carbon warming effect at the tropopause. Roughly two-thirds of the estimated brown carbon forcing occurs above 5 km, although most brown carbon is found below 5 km. The highest radiative absorption occurred during an event that ingested a wildfire plume. We conclude that high-altitude brown carbon from biomass burning is an unappreciated component of climate forcing.
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, United States; Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, United States; Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, United States; Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, VA, United States; Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, United States; Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, United States; Department of Chemistry and Biogeochemistry, University of Colorado Boulder, Boulder, CO, United States; School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, United States; Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Palea Penteli, Greece; Institute for Chemical Engineering Science, Foundation for Research and Technology Hellas, Patra, Greece
Recommended Citation:
Zhang Y.,Forrister H.,Liu J.,et al. Top-of-atmosphere radiative forcing affected by brown carbon in the upper troposphere[J]. Nature Geoscience,2017-01-01,10(7)