Fig. 1

Alveolar (unbroken line) and environmental (dotted line) concentrations used for the statistics (70 groups of molecules): molecules which were significantly more present in the environmental air than in the alveolar air have been excluded (data are reported in ppb). The 22 molecules excluded were the following: M19, M26, M27, M28, M31, M32, M45, M48, M49, M73, M92, M97, M98, M102, M103, M104, M105, M116, M117, M18, M120 and M121