1 Stratospheric Influence on the Composition of the Mid- and Upper- Troposphere over North America sampled by the NASA DC-8 during INTEX A Jack E. Dibb, Eric Scheuer, Robert Talbot Climate Change Research Center, Institute for the Study of Earth, Oceans and Space University of New Hampshire, Durham, NH Melody Avery, ??? NASA Langley Research Center Corresponding Author JED: ph 603 862 3062, fax 603 862 2123, jack.dibb@unh.edu 30 June, 2006 Submitted to the JGR special section on INTEX A ABSTRACT A comprehensive atmospheric chemistry payload was deployed on NASA’s DC- 8 airborne laboratory for the INTEX A campaign in July and August, 2004. In-situ and remote measurements from the DC-8 were made to further understanding of the magnitude and distribution of anthropogenic emissions in North America, the processes exporting these emissions from the continental boundary layer, and the transformations they underwent as they were transported downwind to eastern North America and the Atlantic Ocean. We present the vertical and geographic distributions, and relationships between, 7 Be, O 3 , and HNO 3 in the INTEX A data set. Our objective is to identify stratospherically impacted air masses in the upper troposphere, and to estimate their influence on the composition of the upper troposphere, since unrecognized stratospheric influence may confound efforts to understand the fate of surface emissions lofted to the upper troposphere. Beryllium-7 and the HNO 3 /O 3 ratio identify similar distinct stratospheric and tropospheric populations in the upper troposphere. Stratospherically impacted air was most common over the north eastern portion of the INTEX A study area. Estimates of the impact of stratospheric contributions on the upper tropospheric