Recent observations have shown that anthropogenic pollutants are transported across the Pacific to the west coast of North America on a regular basis. Our previous airborne observations from one campaign in 1999 suggest that the import fluxes to North America are greatest in the free troposphere. However, there are no-ongoing free tropospheric observations for most of the key species in the air arriving to North America. We propose to make observations of CO, O3, aerosol scatter and non-methane hydrocarbons using a small aircraft equipped with appropriate sensors. These observations will be conducted throughout the year, but with an emphasis on the Spring 2002 time period, when the NOAA ITCT experiment on intercontinental transport will take place on the west coast of North America. Along with these aircraft data, we will utilize the GEOS-Chem global chemical transport model to examine the CO and O3 import fluxes into North America from various sources.