Chemical characterization of indoor and outdoor fine particulate matter in an occupied apartment in Rome, Italy.

The daily concentration and chemical composition of PM2.5 was determined in indoor and outdoor 24-h samples simultaneously collected for a total of 5 weeks during a winter and a summer period in an apartment sited in Rome, Italy. The use of a specifically developed very quiet sampler (<35 dB) allowed the execution of the study while the family living in the apartment led its normal life. The indoor concentration of PM2.5 showed a small seasonal variation, while outdoor values were much higher during the winter study. Outdoor sources were found to contribute significantly to indoor PM concentration especially during the summer, when the apartment was naturally ventilated by opening the windows. During the winter the infiltration of outdoor PM components was lower and mostly regulated by the particle dimensions. Organics displayed In/Out ratios higher than unity during both periods; their indoor production increased significantly during the weekends, where the family stayed mostly at home. PM components were grouped into macrosources (soil, sea, secondary inorganics, traffic, organics). During the summer the main contributions to outdoor PM2.5 came from soil (30%), secondary inorganics (29%) and organics (22%). Organics dominated both indoor PM2.5 during the summer (60%) and outdoor and indoor PM2.5 during the winter (51% and 66%, respectively).