Personal exposure to nitrogen dioxide in Switzerland

Home indoor and outdoor levels, and personal exposures to NO2 were determined for more than 500 subjects in a subpopulation of SAPALDIA by using passive samplers. The overall personal NO2 average was found to be 27 μg m−3, the overall indoor average 21 μg m−3 and the overall outdoor average 31 μg m−3. Personal NO2 levels ranged between the outdoor and indoor levels, with the exception of study areas with low NO2 concentrations. In the winter, the indoor/outdoor ratios were lower than in the summer. Outdoor NO2 levels were higher in winter. In some study areas, indoor NO2 levels were lower in the winter than in the summer due to reduced ventilation but this was not consistent. Personal NO2 concentrations were very similar during all seasons. Gas-cooking and smoking were important factors for elevated indoor and personal NO2 levels (contribution: 5 μg m−3, 2 μg m−3, respectively). Personal exposure to NO2 correlated best with the indoor NO2 concentrations.