Determination of stratospheric and anthropogenic contributions to enhanced mid-tropospheric O3 in the tropical western Pacific

Tropospheric O3, an important greenhouse gas, is produced both from anthropogenic precursors and transport from the stratosphere. Previous O3 and water vapor observations in the remote tropical Pacific have shown strongly anti-correlated filaments of high O3 and reduced H2O in the mid-troposphere. These filaments were a pervasive feature seen throughout the troposphere during the CONvective TRansport of Active Species in the Tropics (CONTRAST) campaign. While it has been proposed, based on analysis of prior observations, that these filaments result from stratospheric intrusion, lack of concomitant measurement of atmospheric tracers has limited the ability to quantitatively assess the relative roles of pollution and stratospheric intrusions. In addition to O3, H2O, and CO, tracers for biomass burning, fossil fuel emissions, and the stratosphere were also measured during CONTRAST. Preliminary correlation analysis shows not only frequent anti-correlation between O3 and water vapor in the filaments but also correlation between O3 and CO as well as other anthropogenic and pyrogenic tracers. The filaments appear to be a complex mixture of air parcels from different origins. Analysis of these observations, along with results from global chemistry models and back trajectories, will be discussed, focusing on anthropogenic and stratospheric contributions to tropospheric O3.