Total mass concentration of aerosol layers observed during the flights agrees reasonably well with the CFORS model prediction for the combined mass concentration of dust, sulfate, BC, and organic carbon. BC typically accounts for about 3 percent of the total aerosol mass, so large errors in BC estimates will not affect the agreement significantly. The CFORS modeled BC transport across 130W is nearly twice that of the total United States BC emissions. Analysis of the CFORS transport and subsequent validation by ground measurements of BC compares well in the Western Pacific, but over-predicts BC in the Eastern Pacific by a factor of 3. Reducing the model output by a factor of 3 modifies the estimate of BC mass transport to approximately 25 to 80 percent of US direct emissions, still a substantial quantity. As the model does not include a parameter for wet removal of BC, the discrepancy between model-observation agreement in the West and East Pacific Ocean is a good indicator that BC acquires a hydrophilic coating during transport and is subject to wet removal. The rate of BC removal due to wet scavenging is currently not well parameterized in global climate models (GCM). The present results suggest that wet removal of BC is an important process for representations of BC atmospheric residence time and radiative forcing.
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