1. a Department of Physical Sciences , University of Helsinki , Helsinki , Finland
2. b Department of Occupational and Environmental Health , Stockholm , Sweden
3. c Institut Municipal d’Investigació Mèdica , Barcelona , Spain
4. d Instituto Superiore di Sanità , Rome , Italy
5. e Forschungszentrum Institut f. Epidemiologie , Neuherberg , Germany
6. f Department of Environmental Health, Unit of Environmental health , National Public Health Institute , Kuopio , Finland
7. g Institute of Environmental Medicine, Karolinska Institute , Stockholm , Sweden
8. h Stockholm Air Quality and Noise Analysis , Stockholm , Sweden
9. i Department of Epidemiology , Local Health Authority Rome E , Rome , Italy