Articles | Volume 10, issue 5
Atmos. Chem. Phys., 10, 2091–2115, 2010

Special issue: MILAGRO/INTEX-B 2006

Atmos. Chem. Phys., 10, 2091–2115, 2010

  01 Mar 2010

01 Mar 2010

A regional scale modeling analysis of aerosol and trace gas distributions over the eastern Pacific during the INTEX-B field campaign

B. Adhikary1,2, G. R. Carmichael1, S. Kulkarni1, C. Wei1, Y. Tang1,*, A. D'Allura1,**, M. Mena-Carrasco1,***, D. G. Streets3, Q. Zhang3, R. B. Pierce4,****, J. A. Al-Saadi4, L. K. Emmons5, G. G. Pfister5, M. A. Avery4, J. D. Barrick4, D. R. Blake6, W. H. Brune7, R. C. Cohen8, J. E. Dibb9, A. Fried5, B. G. Heikes10, L. G. Huey11, D. W. O'Sullivan12, G. W. Sachse4, R. E. Shetter5, H. B. Singh13, T. L. Campos5, C. A. Cantrell5, F. M. Flocke5, E. J. Dunlea14,*****, J. L. Jimenez14, A. J. Weinheimer5, J. D. Crounse15, P. O. Wennberg15, J. J. Schauer16, E. A. Stone16, D. A. Jaffe17, and D. R. Reidmiller18 B. Adhikary et al.
  • 1Center for Global and Regional Environmental Research, University of Iowa, Iowa City, IA 52242, USA
  • 2School of Engineering, Kathmandu University, Dhulikhel, Kavre, Nepal
  • 3Decision and Information Sciences Division, Argonne National Laboratory, Argonne, IL, USA
  • 4NASA Langley Research Center, Hampton, VA, USA
  • 5National Center for Atmospheric Research, Boulder, CO, USA
  • 6Department of Chemistry, University of California, Irvine, CA, USA
  • 7Department of Meteorology, Penn State University, University Park, PA, USA
  • 8Department of Chemistry, University of California, Berkeley, CA, USA
  • 9Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH, USA
  • 10Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA
  • 11School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
  • 12United States Naval Academy, Annapolis, MD, USA
  • 13NASA Ames Research Center, Moffett Field, CA, USA
  • 14Department of Chemistry and Biochemistry, and CIRES, University of Colorado, Boulder, CO, USA
  • 15California Institute of Technology, Pasadena, CA, USA
  • 16Environmental Chemistry and Technology, College of Engineering, University of Wisconsin-Madison, Madison, WI, USA
  • 17University of Washington, Bothell, WA 98011, USA
  • 18Department of Atmospheric Sciences/University of Washington, Seattle, WA 98195, USA
  • *now at: NOAA/NCEP/EMC, Camp Springs, MD, USA
  • **now at: ARIANET Srl, Milano, Italy
  • ***now at: Universidad Andrés Bello, Santiago, Chile
  • ****now at: NOAA/NESDIS, Madison, WI, USA
  • *****now at: NOAA Climate Program Office, Silver Spring, MD, USA

Abstract. 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%).

Special issue
Final-revised paper