B Adhikary, Kathmandu University
Gregory R. Carmichael, University of Iowa
S Kulkarni, University of IowaFollow
C Wei, University of Iowa
Y Tang, NOAA
M Mena-Carrasco, University of Iowa
David G. Streets, Argonne National Laboratory
Q Zhang, Argonne National Laboratory
R B. Pierce, NOAA
J Al-Saadi, NASA
L K. Emmons, National Center for Atmospheric Research
G G. Pfister, National Center for Atmospheric Research
M A. Avery, NASAFollow
J D. Barrick, NASA
D R. Blake, University of California, Irvine
William H. Brune, Pennsylvania State University - Main Campus
Robert C. Cohen, University of California - Berkeley
Jack E. Dibb, University of New HampshireFollow
A Fried, University of Colorado Boulder
B J. Heikes, University of Rhode Island
L Gregory Huey, Georgia Institute of Technology - Main Campus
D W. O'Sullivan, United States Naval Academy
G W. Sachse, NASA Langley Research CenterFollow
R E. Shetter, NOAA
H B. Singh, NASA
T L. Campos, National Center for Atmospheric Research
C A. Cantrell, National Center for Atmospheric Research
F Flocke, National Center for Atmospheric Research
E J. Dunlea, University of Colorado Boulder
Jose L. Jimenez, University of Colorado BoulderFollow
Andrew Weinheimer, National Center for Atmospheric Research
John D. Crounse, Southern California Institute of Technology
Paul Wennberg, California Institute of Technology
James J. Schauer, University of Wisconsin-Madison
E A. Stone, University of Wisconsin-Madison
D A. Jaffe, University of Washington - Bothell Campus
D R. Reidmiller, University of Washington - Seattle Campus


The Sulfur Transport and dEposition Model (STEM) is applied to the analysis of observations obtained during the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B), conducted over the eastern Pacific Ocean during spring 2006. Predicted trace gas and aerosol distributions over the Pacific are presented and discussed in terms of transport and source region contributions. Trace species distributions show a strong west (high) to east (low) gradient, with the bulk of the pollutant transport over the central Pacific occurring between ∼20° N and 50° N in the 2-6 km altitude range. These distributions are evaluated in the eastern Pacific by comparison with the NASA DC-8 and NSF/NCAR C-130 airborne measurements along with observations from the Mt. Bachelor (MBO) surface site. Thirty different meteorological, trace gas and aerosol parameters are compared. In general the meteorological fields are better predicted than gas phase species, which in turn are better predicted than aerosol quantities. PAN is found to be significantly overpredicted over the eastern Pacific, which is attributed to uncertainties in the chemical reaction mechanisms used in current atmospheric chemistry models in general and to the specifically high PAN production in the SAPRC-99 mechanism used in the regional model. A systematic underprediction of the elevated sulfate layer in the eastern Pacific observed by the C-130 is another issue that is identified and discussed. Results from source region tagged CO simulations are used to estimate how the different source regions around the Pacific contribute to the trace gas species distributions. During this period the largest contributions were from China and from fires in South/Southeast and North Asia. For the C-130 flights, which operated off the coast of the Northwest US, the regional CO contributions range as follows: China (35%), South/Southeast Asia fires (35%), North America anthropogenic (20%), and North Asia fires (10%). The transport of pollution into the western US is studied at MBO and a variety of events with elevated Asian dust, and periods with contributions from China and fires from both Asia and North America are discussed. The role of heterogeneous chemistry on the composition over the eastern Pacific is also studied. The impacts of heterogeneous reactions at specific times can be significant, increasing sulfate and nitrate aerosol production and reducing gas phase nitric acid levels appreciably (∼50%).


Earth Sciences, Earth Systems Research Center

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Atmospheric Chemistry and Physics


Copernicus Publications

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© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License.