1 Department of Pneumology, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
2 Institute and Outpatient Clinic for Occupational, Social and Environmental Medicine, Clinical Centre of the Ludwig Maximilian University Munich, Munich, Germany.
3 Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA.
4 Department of Pneumology, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany. Electronic address: gernot.zissel@uniklinik-freiburg.de.