Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.A Portable Emissions Measurement System (PEMS) is essentially a lightweight laboratory'' that is used to test and/or assess mobile source emissions (i.e. cars, trucks, buses, construction equipment, generators, trains, cranes, etc.) for the purposes of compliance, regulation, or decision-making. Governmental entities like the United States Environmental Protection Agency (USEPA), the European Union, as various states and private sector entities have begun to utilize PEMS in order to reduce both the costs and time of mobile emissions decisions. Various state, federal, and international agencies began referring to this shorthand term in early 2000, and the nickname became part of industry parlance.