INtercontinental Chemical Transport EXperiment - Phase B (INTEX-B) is an integrated atmospheric field experiment performed over North America from March 1 to May 15, 2006. The first phase of the study in March will focus on Mexico City pollution outflow. The second phase during April and May will focus on Asian pollution outflow. It seeks to understand the transport and transformation of gases and aerosols on transcontinental/intercontinental scales and their impact on air quality and climate. A particular focus in this study is to quantify and characterize the inflow and outflow of pollution over North America. The main constituents of interest are ozone and precursors, aerosols and precursors, and the longlived greenhouse gases.