A comprehensive aircraft observation data set was obtained during the TRACE-P (TRAnsport and Chemical Evolution over the Pacific) field campaign. These observations complement ground and satellite data, and together provide a detailed characterization of the dynamical and chemical processes affecting the atmospheric composition in East Asia. This current study applies a four-dimensional variational data assimilation technique (4D-Var) to the observational data using the STEM-III (Sulfate Transport Eulerian Model) chemistry transport model. The impacts of different chemical components on ozone concentrations are examined through adjoint sensitivity analysis. With detailed sensitivity results of various chemical components available in the full space and entire time window, the adjoint sensitivity analysis yields insight in to how to build future observations more effectively. Finally, the observational data are assimilated to give a more complete picture of the chemical and dynamical evolution of the Asian outflow over the west Pacific, with tropospheric ozone as the focus.