THIS PROJECT PROPOSES TO USE AIRCRAFT (ATOM HIPPO AND ATTREX) AND GROUND-BASED SF6 AND OTHER SHORTER LIVED TRACER OBSERVATIONS (NOAA-AGAGE NETWORK) TO MEASURE THE DISTRIBUTION OF TRANSPORT TIMESCALES OF NORTHERN MID-LATITUDE SURFACE LEVEL AIR TO THE SOUTHERN HEMISPHERE. IN ADDITION EVALUATION AND IMPROVE MODEL PREDICTIONS OF THE SAME QUANTITIES WITHIN GLOBAL CHEMICAL TRANSPORT MODELS (GEOS AND GISS-MODELE) MODELS DESIGNED TO SIMULATE BOTH SHORT (SUB-SEASONAL-DECADES) TO LONG TIMESCALES (CENTURIES).