Source apportionment, geochemical characterization, and inhalation health-risk assessment of PM2.5 in Tabriz and Urmia, northwestern Iran

Desiccation of Lake Urmia may expose nearby cities to lakebed dust, but source-resolved evidence is lacking. The elemental composition of PM 2.5 (particulate matter with aerodynamic diameter < 2.5 μm) sampled weekly from March to December 2024 in the metropolitan areas of Tabriz (TBR) and Urmia (URM), northwestern Iran, were characterized through combining Positive Matrix Factorization (PMF), geochemical indices and United States Environmental Protection Agency health risk assessment (USEPA). PMF resolved seven factors per site. Lake Urmia lakebed dust was the largest source at TBR (32.20% of PM 2.5 ; Ti loading 85.80% of species sum) and the main geogenic source at URM (16.60%; Na/K/Mg-dominated), a contrast consistent with size-selective aeolian fractionation. Industrial/heavy oil combustion (29.80%) at TBR and traffic exhaust (22.00%) at URM led the anthropogenic contributions. EF and I geo showed extreme enrichment of Zn, Ba, and Ag at both cities, with Cd, Sb, and Mo additionally extremely enriched at URM. Contamination indices were higher at URM (PLI = 4.63; mCd = 63.83; IPI = 1080.60) than at TBR (PLI = 1.00; mCd = 33.42; IPI = 783.04), but these values mainly reflect the halite-evaporitic background of lakebed dust, a bias of crust-normalized indices shown here for a hypersaline terminal-lake setting, rather than literal pollution levels. Adult Incremental Lifetime Cancer Risk (ILCR) at TBR (1.43 × 10⁻⁶) fell within the USEPA tolerable range (1 × 10⁻⁶–1 × 10⁻⁴), and chromium, assumed fully Cr(VI) an upper bound, contributed 96.2% (TBR) and 87.7% (URM) of total ILCR; PMF attributed this chromium mainly to non-exhaust traffic emissions, whereas arsenic dominated the non-chromium fraction. MANOVA and Linear Discriminant Analysis (LDA) indicated strong compositional divergence between the cities. Traffic control and industrial arsenic abatement are the most actionable regulatory targets.