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AGU: Geophysical Research Letters

 

Index Terms

  • Atmospheric Composition and Structure: Aerosols and particles
  • Atmospheric Composition and Structure: Troposphere: composition and chemistry
  • Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry
  • Atmospheric Composition and Structure: Radiation: transmission and scattering
  • Geographic Location: Asia

Abstract

A large organic aerosol source in the free troposphere missing from current models

Colette L. Heald

Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA

Daniel J. Jacob

Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA

Rokjin J. Park

Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA

Lynn M. Russell

Scripps Institution of Oceanography, University of California, La Jolla, California, USA

Barry J. Huebert

Department of Oceanography, University of Hawaii at Manoa, Honolulu, Hawaii, USA

John H. Seinfeld

Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

Hong Liao

Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

Rodney J. Weber

School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA

Aircraft measurements of organic carbon (OC) aerosol by two independent methods over the NW Pacific during the ACE-Asia campaign reveal unexpectedly high concentrations in the free troposphere (FT). Concentrations average 4 μg sm−3 in the 2–6.5 km column with little vertical gradient. These values are 10–100 times higher than computed with a global chemical transport model (CTM) including a standard 2-product simulation of secondary organic aerosol (SOA) formation based on empirical fits to smog chamber data. The same CTM reproduces the observed vertical profiles of sulfate and elemental carbon aerosols, which indicate sharp decreases from the boundary layer to the FT due to wet scavenging. Our results suggest a large, sustained source of SOA in the FT from oxidation of long-lived volatile organic compounds. We find that this SOA is the dominant component of aerosol mass in the FT, with implications for intercontinental pollution transport and radiative forcing of climate.

Received 20 June 2005; accepted 24 August 2005; published 27 September 2005.

Citation: Heald, C. L., D. J. Jacob, R. J. Park, L. M. Russell, B. J. Huebert, J. H. Seinfeld, H. Liao, and R. J. Weber (2005), A large organic aerosol source in the free troposphere missing from current models, Geophys. Res. Lett., 32, L18809, doi:10.1029/2005GL023831.

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