Source apportionment of PM10 and its oxidative potential in urban residential areas

The assessment of the contribution of atmospheric particulate matter (PM) emission sources and their possible health effects in indoor environments is crucial because most of our time is spent indoors [1]. However, the valuation of air quality in residential environments is complex because it depends not only on the several indoor sources but also on the PM emitted by outdoor sources that penetrate inside buildings. In this study,15 apartments situated in the urban area of Rome were examined, selected on the basis of their different locations with respect to urban PM sources (e.g. traffic, domestic heating) and the presence of different indoor emissionsources (e.g. cigarette smoke, use of incense and small household appliances with brush motors). At each site, both indoor and outdoor PM10 was sampled for two consecutive years by bimonthly sampling using very low flow rate instrumentation (0.5 L min-1). Samples were analysed by more than 100 chemical variables: PM10, ions, macro-elements, water soluble and residual fraction of trace elements, levoglucosan, elemental carbon and organic carbon. The application of Positive Matrix Factorisation (PMF) on the chemical characterisation data made it possible to identify 8 prevalent emission sources and to assess their contribution to PM10 [2] and its oxidative potential (measured by DCFH, AA and DTT acellular assays) in the indoor and outdoor environments of each site. Outdoor PM10 concentrations were quite similar between the sites, showing a clear seasonal pattern [3], with peak concentrations in the winter months, and a spatial variability mainly related to the different micro-locations of the sites: distance from busy roads, presence oftram or railway tracks, street or backyard exposure. Soil dust and domestic biomass heating were the emission sources with the greatest contribution to PM10 in outdoor environments, in summer and winter respectively. In contrast, PM10 concentrations in indoor environments showed greater site-specific variability. Cigarette smoke, when present, is the source that showed the highest contribution to PM10 in indoor environments. Compared to outdoor air, indoor results showed a general decrease in contributions to PM10 from soil dust, sea spray and vehicular traffic. Principal component analysis (PCA) allowed the oxidative potential assays to be associated with the different chemical composition and thus the different emission sources of PM10. DCFH assay was sensitive to all combustive sources, in particular cigarette smoke and indoor incense use, while DTT and AA were sensitive to biomass combustion for domestic heating and non combustive vehicular traffic, respectively. These results increase the understanding of the complex dynamics influencing indoor air quality, underlining the significance of including its assessment in inhalation exposure studies.