Expanding the chemical space of urban air: Identification and semiquantification of polar emerging contaminants in PM2.5 through LC-HRMS non-target analysis.

Fine particulate matter (PM₂.₅) is associated with severe human health effects, yet its organic fraction remains only partially characterized. This study aimed to expand the current understanding of airborne contaminants of emerging concern (CECs) in urban PM₂.₅ using liquid chromatography-high-resolution mass spectrometry (LC-HRMS)-based non-target analysis (NTA). PM₂.₅ samples were collected from eight monitoring stations across Barcelona (Spain) representing traffic, urban background, and port areas. After pressurized liquid extraction, samples were analysed by data-dependent LC-HRMS, followed by suspect screening and semiquantification. A total of 40 CECs were confidently annotated (identification level 2 A), including industrial chemicals, personal care products, pesticides, pharmaceuticals, and drugs of abuse. To our knowledge, 21 compounds are reported for the first time in urban air. Concentrations generally ranged from pg/m⁻³ to ng/m⁻³ , with industrial chemicals (e.g., dicyclohexylamine, tributyl phosphate) and the repellent N,N-diethyl-m-toluamide (DEET) reaching the highest levels. Several identified compounds are classified as irritants, endocrine disruptors, or suspected carcinogens. Transformation products and metabolites were also detected. These findings reveal the ubiquity and chemical diversity of organic CECs in urban PM₂.₅, highlighting their potential relevance for human health and their likely role as a pathway for environmental contamination via atmospheric deposition.