Two-year monitoring of indoor and outdoor PM10 at 15 sites in an urban setting. Part I: chemical composition and source tracers

Simultaneous measurements of PM 10 and more than 80 chemical components have been carried out indoors and outdoors at 15 residential sites in the urban area of Rome, Italy, for a study period of 2 years from May 2019 to April 2021 (12 samplings of the duration of 2 months each). Outdoor PM 10 concentrations were rather homogeneous over the territory (range 18–30 μg/m 3 ) and the ranking of the sites was relatively constant during the whole study, while much more marked differences among the dwellings were recorded indoors (range 11–125 μg/m 3 ), with indoor/outdoor ratios up to over 4. Using the water-soluble or insoluble fractions of some elements as source tracers allowed the identification of specific indoor sources in some of the dwellings: cigarette smoking - by far the one with the highest influence on indoor PM concentration -, biomass burning, burning of candles and incense and use of appliances operated by brush electric motors. Non-exhaust emission of vehicular traffic was detected by the insoluble fraction of Cu, Mo, Sb, Sn, and Zr. The outdoor concentration of these particles was influenced mainly by the centrality of the area, its height above sea level, and the overlook of the apartments, while their indoor penetration was mainly dependent on the characteristics of the building. Lower concentrations, particularly of traffic tracers, were detected during the second year of the study due to the restrictions during the pandemic. • Indoor and outdoor PM 10 was characterised at 15 urban sites for 2 years (360 samples). • Long-term samplings (2 months) well represented the characteristics of the site. • Outdoor PM 10 showed little variations over the territory and covariance among sites. • Indoor concentration and composition were variable and dependent on specific sources. • I/O ratios were dependent on the characteristics of the buildings.