A comparison of size distribution and chemical composition of fine particles in residential and traffic sites

摘要

Background. Exposure to air pollution from traffic is a major public health concern. Aims. The objective of the study is the improvement of the characterization of indoor and outdoor population exposure to traffic pollutants. Methods. The measurement campaigns were carried out in the urban area of Bologna, a highly polluted city in northern Italy. Both indoor and outdoor monitoring was simultaneously carried out at a residential setting as well as at a heavy traffic site. Indoor environments were uninhabited, very similar in terms of volumes and building materials, and air exchange rates were maintained at the fixed value of 0.5 h-1, a typical level for residential environments. The main goal was to assess the differences of population exposure to particles in relation to traffic without considering the specific indoor characteristics and personal behaviours. Both sites were monitored during threel5-day periods, suitably distributed to cover the different seasons. We collected data on mass and chemical composition (ions, organic and elemental carbon, metals) of PM2.5. Two FMPSs (TSI) provided size distribution of particles in the 5.6-560 nm interval with 1-min time resolution. Two switching units, one for each site, alternatively activated indoor and outdoor inflow with a switch time of 10 min. Results. While we found very similar PM2.5 mass concentrations in the two monitoring sites, chemical composition and ultra-fine particles (UFP) showed large differences. UFP outdoor concentrations in the traffic site were almost twice as much as the residential site. Indoor UFP concentrations were much lower than outdoor with a ratio between the two sites similar to outdoor concentration ratio. Indoor/outdoor ratio showed an inverse relation with outdoor concentrations. Size distribution showed a strong multi-modality with relevant differences between the two sites. Conclusions. We found marked differences of UFP between the traffic and the residential site in both indoor and outdoor levels. Very little differences were found for PM2.5 mass.