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Summertime influence of Asian pollution in the free troposphere over North America
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Division of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, USA
NASA Langley Research Center, Hampton, Virginia, USA
NASA Langley Research Center, Hampton, Virginia, USA
NASA Langley Research Center, Hampton, Virginia, USA
Department of Chemistry, University of California, Irvine, California, USA
Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA
Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania, USA
Department of Chemistry, University of California, Berkeley, California, USA
Climate Change Research Center, University of New Hampshire, Durham, New Hampshire, USA
Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA
Department of Meteorology, Florida State University, Tallahassee, Florida, USA
Department of Meteorology, Florida State University, Tallahassee, Florida, USA
Department of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
NASA Ames Research Center, Moffett Field, California, USA
California Institute of Technology, Pasadena, California, USA
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 NOy species in the Asian plumes is dominated by PAN (∼600 pptv), with varying NOx/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, NOx, HNO3, and O3 reflecting active photochemistry, possibly enhanced by efficient NOy 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 NOx.
Received 15 August 2006; accepted 11 January 2007; published 11 May 2007.
Citation: (2007), Summertime influence of Asian pollution in the free troposphere over North America, J. Geophys. Res., 112, D12S11, doi:10.1029/2006JD007919.
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