Characteristics of the exposures to source-specific ambient VOCs in Lagos, Nigeria

This study characterized the concentrations, spatial and seasonal patterns, and sources of ambient volatile organic compounds (VOCs) at six sites in Lagos, Nigeria from August 2020 to July 2021. VOC samples were collected twice per month using Summa canisters and analyzed by gas chromatography-mass spectrometry (GC-MS). Marked spatial variability was observed: IKO had the highest median total VOC (TVOC) concentration (104 ppbv) and the coastal, suburban NCF site was lowest (29 ppbv). Ethane, naphthalene, propane, and ethylene were the most abundant individual species across the monitoring network. Network-wide TVOC was 17% higher during the dry season (median 60 vs 51 ppbv), although this difference was not statistically significant, indicating that most VOC sources operate year-round. Positive Matrix Factorization (PMF) resolved nine source factors: Gasoline Evaporation (5.33%), Polymer/Refrigerant (8.28%), Foam Blowing (6.94%), DCM Solvent Use (14.22%), Oxygenated Solvents (12.86%), Paint/Aromatic Solvents (7.95%), Vehicle Exhaust (20.33%), Waste/Biomass Burning (14.92%), and LPG/Urban Background (9.16%). Combustion-related sources contributed 35% and non-combustion sources (solvent use and evaporative emissions) 65% of TVOC. All nine factors exhibited statistically significant spatial heterogeneity across the sites (Kruskal-Wallis, p < 0.001). Directional and back-trajectory analyses confirmed predominantly S-SSW transport footprints, linking vehicle exhaust to major expressway corridors and waste/biomass burning to two distinct source zones: the western Mainland corridor and the eastern Lekki coastal zone. Correlation analysis with combustion tracers (CO, NOx and CH₄) confirmed that non-combustion sources dominate the VOC burden in Lagos. These findings provide the first source-resolved VOC evidence base for Lagos, supporting targeted emission controls across both combustion and solvent/industrial sectors.