Summertime influence of Asian pollution in the free troposphere over North America

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Read Full Article (file size: 14569783 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D12S11, doi:10.1029/2006JD007919, 2007 Summertime influence of Asian pollution in the free troposphere over North America Q. Liang Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA L. Jaeglé Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA R. C. Hudman Division of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, USA S. Turquety Division of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, USA D. J. Jacob Division of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, USA M. A. Avery NASA Langley Research Center, Hampton, Virginia, USA E. V. Browell NASA Langley Research Center, Hampton, Virginia, USA G. W. Sachse NASA Langley Research Center, Hampton, Virginia, USA D. R. Blake Department of Chemistry, University of California, Irvine, California, USA W. Brune Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA X. Ren Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA R. C. Cohen Department of Chemistry, University of California, Berkeley, California, USA J. E. Dibb Climate Change Research Center, University of New Hampshire, Durham, New Hampshire, USA A. Fried Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA H. Fuelberg Department of Meteorology, Florida State University, Tallahassee, Florida, USA M. Porter Department of Meteorology, Florida State University, Tallahassee, Florida, USA B. G. Heikes Department of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA G. Huey School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA H. B. Singh NASA Ames Research Center, Moffett Field, California, USA P. O. Wennberg California Institute of Technology, Pasadena, California, USA Abstract We analyze aircraft observations obtained during INTEX-A (1 July to 14 August 2004) to examine the summertime influence of Asian pollution in the free troposphere over North America. By applying correlation analysis and principal component analysis (PCA) to the observations between 6 and 12 km, we find dominant influences from recent convection and lightning (13% of observations), Asia (7%), the lower stratosphere (7%), and boreal forest fires (2%), with the remaining 71% assigned to background. Asian air masses are marked by high levels of CO, O₃, HCN, PAN, C₂H₂, C₆H₆, methanol, and SO₄ ^2–. The partitioning of NO_y species in the Asian plumes is dominated by PAN (∼600 pptv), with varying NO_x/HNO₃ ratios in individual plumes, consistent with individual transit times of 3–9 days. Export of Asian pollution occurred in warm conveyor belts of midlatitude cyclones, deep convection, and in typhoons. Compared to Asian outflow measurements during spring, INTEX-A observations display lower levels of anthropogenic pollutants (CO, C₃H₈, C₂H₆, C₆H₆) due to shorter summer lifetimes; higher levels of biogenic tracers (methanol and acetone) because of a more active biosphere; and higher levels of PAN, NO_x, HNO₃, and O₃ reflecting active photochemistry, possibly enhanced by efficient NO_y export and lightning. The high ΔO₃/ΔCO ratio (0.76 mol/mol) in Asian plumes during INTEX-A is due to strong photochemical production and, in some cases, mixing with stratospheric air along isentropic surfaces. The GEOS-Chem global model captures the timing and location of the Asian plumes. However, it significantly underestimates the magnitude of observed enhancements in CO, O₃, PAN and NO_x. Received 15 August 2006; accepted 11 January 2007; published 11 May 2007. Keywords: intercontinental transport; Asia; ozone. Index Terms: 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry. Read Full Article (file size: 14569783 bytes) Cited by Citation: Liang, Q., et al. (2007), Summertime influence of Asian pollution in the free troposphere over North America, J. Geophys. Res., 112, D12S11, doi:10.1029/2006JD007919. Copyright 2007 by the American Geophysical Union.

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