The ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) is a framework for investigation of the atmospheric chemistry of mixed urban/biogenic air masses. The research is conducted primarily through a comprehensive, multi-platform field campaign near Paris, in which observations will be made to address key scientific questions, but also includes related laboratory and modeling activities. The purpose of this townhall meeting is to present information about ACROSS and to answer questions from scientists who are interested in being involved in the project.