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There is increasing evidence that Asian emissions from fossil fuel combustion and biomass burning have a pervasive impact on the composition of the Pacific troposphere, affecting aerosol levels and ozone photochemistry as far as the west coast of the United States. Estimates of this intercontinental transport of air pollution remain highly uncertain, and the mechanisms for this transport are still poorly understood.

We are in the process of analyzing and modeling observations from recent field missions to reduce uncertainties in evaluating the current and future effects of Asian outflow on the Northeast Pacific and the global atmosphere. Our work is based on using the GEOS-CHEM 3-D model of tropospheric chemistry.

We have analyzed surface observations at Cheeka Peak Observatory and at ground sites throughout the North Pacific using the GEOS-CHEM global tropospheric chemistry model to examine the seasonal variations of Asian long-range transport. Asian influence on CO levels in the North Pacific troposphere maximizes during spring and minimizes during summer. The model successfully captures a number of strong trans-Pacific transport events reaching the US west coast [Jaegle et al., 2003; Weiss-Penzias et al., 2004; Bertschi et al., 2004; Liang et al., 2004].

In a study which was recently submitted to the Journal of Geophysical Research [Liang et al., 2005] we developed three empirical meteorological indices based on sea-level pressure, to capture variations in transpacific transport on daily to interannual timescales.

Several transpacific transport events with significant enhancements in CO, O3, PAN, aerosols were observed over the United States during the NASA INTEX-A field mission taking place in the summer of 2004. We are using the GEOS-CHEM model to understand the meteorological mechanisms and chemical evolution of these plumes.