Sunyer J, Jarvis D, Gotschi T, Garcia-Esteban R, Jacquemin B, Aguilera I, Ackerman U, de Marco R, Forsberg B, Gislason T, Heinrich J, Norback D, Villani S, Kunzli N. Chronic bronchitis and urban air pollution in an international study. Occup Environ Med. 2006 Dec;63(12):836-43. doi: 10.1136/oem.2006.027995