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Published October 16, 2004 | Published
Journal Article Open

Three-dimensional simulations of inorganic aerosol distributions in east Asia during spring 2001


In this paper, aerosol composition and size distributions in east Asia are simulated using a comprehensive chemical transport model. Three-dimensional aerosol simulations for the TRACE-P and ACE-Asia periods are performed and used to help interpret actual observations. The regional chemical transport model, STEM-2K3, which includes the on-line gas-aerosol thermodynamic module SCAPE II, and explicitly considers chemical aging of dust, is used in the analysis. The model is found to represent many of the important observed features. The Asian outflow during March and April of 2001 is heavily polluted with high aerosol loadings. Under conditions of low dust loading, SO_2 condensation and gas phase ammonia distribution determine the nitrate size and gas-aerosol distributions along air mass trajectories, a situation that is analyzed in detail for two TRACE-P flights. Dust is predicted to alter the partitioning of the semivolatile components between the gas and aerosol phases as well as the size distributions of the secondary aerosol constituents. Calcium in the dust affects the gas-aerosol equilibrium by shifting the equilibrium balance to an anion-limited status, which benefits the uptake of sulfate and nitrate, but reduces the amount of aerosol ammonium. Surface reactions on dust provide an additional mechanism to produce aerosol nitrate and sulfate. The size distribution of dust is shown to be a critical factor in determining the size distribution of secondary aerosols. As much of the dust mass is found in the supermicron mode (70–90%), appreciable amounts of sulfate and nitrate are found in the supermicron particles. For sulfate the observations and the analysis indicate that 10–30% of sulfate is in the supermicron fraction during dust events; in the case of nitrate, more than 80% is found in the supermicron fraction.

Additional Information

Copyright 2004 by the American Geophysical Union. Received 1 October 2003; revised 15 February 2004; accepted 24 February 2004; published 25 August 2004. We appreciate Marco Rodriguez (University of California at Irvine) for his help on the SCAPE source code conversion. This work was supported in part by grants from the NSF Atmospheric Chemistry Program, NSF grant Atm-0002698, NASA GTE and ACMAP programs, and the Department of Energy Atmospheric Chemistry Program. This work (Itsushi Uno) was also partly supported by Research and Development Applying Advanced Computational Science and Technology (ACT-JST) and the CREST of Japan Science and Technology Corporation. Barry Huebert's contribution to this work was supported by National Science Foundation grants ATM0002698 and ATM0002604. This research is a contribution to the International Global Atmospheric Chemistry (IGAC) Core Project of the International Geosphere Biosphere Program (IGBP) and is part of the IGAC Aerosol Characterization Experiments (ACE).

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