Assessment of PM₁ in indoor and outdoor environments: Elemental composition, sources and their implications for...

This study presents an integrated assessment of fine particulate matter present in indoor and outdoor environments within the Metropolitan Area of Mexico City (MAMC), combining PM₁ chemical characterization, PM_2.5 concentrations, real-time particle exposure, source apportionment, and non-carcinogenic inhalation risk assessments. Measurements were conducted at residential and university sites to evaluate spatial variability, indoor-outdoor concentrations. No significant differences were observed between indoor and outdoor PM concentrations; however, site-resolved analysis revealed variability across locations. Organic carbon dominated PM₁ composition, followed by S, Si, Al, K, and elemental carbon. Statistical analysis of indoor/outdoor ratios indicated an outdoor dominance for crustal and secondary elements (Al, Ca, Fe, Si, S), while most species showed comparable indoor/outdoor concentrations. Source apportionment identified distinct profiles outdoors and more mixed contributions indoors, reflecting the coexistence of indoor and outdoor-related PM components. Real-time measurements of lung-deposited surface area showed pronounced short-term increases during combustion-related activities, particularly cooking and gas water heater operation, whereas non-combustion activities had minor effects. Non-carcinogenic risk assessment indicated higher cumulative hazard indices indoors than outdoors, although values remained below the reference threshold (HI < 1). Mn and Pb were identified as the main contributors to potential risk. The results indicate complex PM₁ composition patterns across both indoor and outdoor environments, supporting the integration of chemical composition in air quality assessments.