Four DC-8 flights during Pacific Exploratory Mission (PEM)-Tropics B are analyzed in terms of geographical location, meteorological conditions, and chemical compositions. The meteorological conditions are determined using the meteorological analysis of the Florida State University Global Spectral Model, trajectory analysis, and in situ measurements. Typical undisturbed meteorological conditions are found over the northeastern Pacific between 30¿ and 15¿N and southeast of Hawaiian Islands during flights 5 and 6. Disturbed meteorological conditions are found over western and central equatorial Pacific especially over the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ) during flights 7 and 10. Comparison of the chemical concentrations between disturbed and undisturbed regions revealed remarkable differences. The distribution of the chemical constituents is found to be closely linked to the atmospheric state. Large amounts of pollutants are found to be capped at lower levels due to climatologically persistent trade wind inversion in the undisturbed regions. Transient convective systems are found to be the primary entity that destroys the inversion, causing the vertical transport of the chemicals. The disturbed regions displayed more homogeneous vertical distributions of chemicals resulting from low-level convergence and associated convection. Trajectory analysis showed that in undisturbed regions centered north of Hawaiian Islands, and in disturbed regions, the interaction between lower-level easterlies and upper-level westerlies plays a significant role on atmospheric chemistry over these regions.