Two-year monitoring of indoor/outdoor PM10 at 15 sites in an urban setting. Part II source apportionment and oxidative potential

Two-year monitoring of indoor and outdoor PM10 was carried out at 15 residential sites in the urban area of Rome, Italy (May 2019–April 2021) through 12 continuous two-month samplings. PM10 source apportionment identified nine emission sources: cigarette smoke, biomass burning, vehicular traffic, road dust, soil dust, heavy oil combustion, ammonium nitrate, and sulphate. The major contributions to outdoor PM10 were from biomass burning in winter and from traffic, especially its non-exhaust component (i.e., brake and road dust), which showed high inter-site variability due to the different micro-locations of the 15 dwellings. Cigarette smoke, where present, was the major indoor source that caused high variability of indoor PM10 among sites. The indoor/outdoor ratio of the identified source contributions indicated that combustion sources showed a great ability to penetrate indoor environments, while coarse particles from road dust, soil dust, and sea spray showed a lower capacity to enter indoors. Principal component analysis (PCA) allowed exploring relationships between the OP values and the chemical composition and sources of PM10. Cigarette smoke, biomass burning-related sources, and non-exhaust traffic were found to be the major contributors to OPDCFH, OPDTT, and OPAA, respectively, revealing the high potential health impact of PM released from some indoor sources.