INTEX-NA is a two phase experiment that aims to understand the transport and transformation of gases and aerosols on transcontinental/intercontinental scales and assess their impact on air quality and climate. The primary constituents of interest are ozone and precursors, aerosols and precursors, and the long-lived greenhouse gases. The first phase (INTEX-A) was completed in the summer of 2004 and the second phase (INTEX-B) is to be performed in the spring of 2006. This document is intended to provide an update on the goals of INTEX-B and define its implementation strategy. The scientific goals envisioned here are based on the joint implementation of INTEX-B, MIRAGE-Mex and DLR/IMPACT studies and their coordination with satellite observations. In collaboration with these partners, the main goals of INTEX-B are to:- Quantify the transpacific transport and evolution of Asian pollution to North America and assess its implications for regional air quality and climate; - Quantify the outflow and evolution of gases and aerosols from the Mexico City Megaplex; - Investigate the transport of Asian and North America pollution to the eastern Atlantic and assess its implications for European air quality; - Validate and refine satellite observations of tropospheric composition; - Map emissions of trace gases and aerosols and relate atmospheric composition to sources and sinks.The INTEX-B field study is to be performed during an approximate 8-week period from March 1 to April 30, 2006.