HFC-365mfc (1,1,1,3,3-pentafluorobutane) is an industrial chemical used for polyurethane foam blowing. From early 2003, HFC-365mfc has been commercially produced as a substitute for HCFC-141b, whose use in Europe has been banned since January 2004. We describe the first detection of HFC-365mfc in the atmosphere and report on a 2 year long record at the high Alpine station of Jungfraujoch (Switzerland) and the Atlantic coast station of Mace Head (Ireland). The measurements at Jungfraujoch are used to estimate the central European emissions of HFC-365mfc, HCFC-141b, and CFC-11. For HFC-365mfc, we estimate the central European emissions (Germany, France, Italy, Switzerland, The Netherlands, Belgium, and Luxembourg) in 2003 and 2004 as 400−500 tonnes year^-1. These emissions are about one-third lower on a per capita basis than what we estimate from the Mace Head measurements for the total of Europe. The estimated emissions of HCFC-141b for central Europe are higher (i.e., 7.2−3.5 ktonnes year^-1) with a decreasing trend in the period from 2000 to 2004. Residual emissions of CFC-11 are estimated at 2.4-4.7 ktonnes year^-1 in the same time period. The Po Valley (northern Italy) appears to be a main source region for HFC-365mfc and for the former blowing agents HCFC-141b and CFC-11. In 2004, the emissions of HFC-365mfc arose from a wider region of Europe, which we attribute to an increased penetration of HFC-365mfc into the European market.