Indoor and outdoor PM2.5 concentrations, sources and their influencing factors in homes and apartments in Santiago, Chile

Abstract

Santiago, Chile, is a polluted South American megacity with respect to ambient fine particulate matter (PM2.5), raising concerns about indoor exposure. Outdoor and indoor PM2.5 concentrations were measured in 28 apartments and 32 houses in Santiago between November 2021 and April 2022 (excluding February) using PurpleAir monitors. Mean PM2.5 concentrations were higher in houses (13.5 mu g/m(3) indoors, 13.6.0 mu g/m(3) outdoors) than in apartments (11.7 mu g/m(3) indoors, 11.4 mu g/m(3) outdoors). The highest average outdoor concentration was observed in autumn (14.7 mu g/m(3)). Outdoor measurements were calibrated against a reference monitoring station. To properly analyze data collected at different locations and periods, all concentrations were dispersion normalized. A novel pattern-recognition technique, FUzzy SpatioTemporal Apportionment (FUSTA), was applied to identify source-related patterns contributing to total PM2.5 in indoor and outdoor environments. The method assumes that indoor PM2.5 includes an indoor-generated pattern with no outdoor counterpart. Six major source-related outdoor/indoor patterns were identified: intermittent sources (17.4/17.5 mu g/m(3)), followed by mountain-valley recirculation (3.2/3.1 mu g/m(3)), regional (3.2/2.4 mu g/m(3)), residential heating (3.1/2.9 mu g/m(3)), secondary aerosols (3/2.9 mu g/m(3)), and traffic (2.5/1.9 mu g/m(3)), respectively. The mean indoor-generated PM2.5 concentration was 2.0 mu g/m(3). Indoor generated PM2.5 levels were significantly higher in homes with smoking (p < 0.01), while cooking was associated with higher concentrations but was not statistically significant (p = 0.3); homes with and without pets had similar concentrations. FUSTA-derived contributions should not be interpreted as chemically resolved source apportionment, but as relative contributions of meteorologically driven spatiotemporal patterns in concentrations, associated with dominant emission sources and atmospheric processes.