Empirical Assessment of Polycyclic Aromatic Hydrocarbon Distribution and Source Apportionment in Urban Atmospheric Particulate Matter in Port Harcourt, Rivers State

Port Harcourt, Rivers State, experiences chronic atmospheric pollution attributable to oil and gas flaring, vehicular emissions, and industrial activities, yet robust empirical data on polycyclic aromatic hydrocarbon speciation and source apportionment in ambient particulate matter remain sparse. This study empirically characterises PAH concentrations associated with PM2.5 and PM10 fractions collected seasonally at six monitoring sites across Port Harcourt using high-volume cascade impactor samplers. Samples were extracted by Soxhlet technique and analysed by gas chromatography-mass spectrometry for 16 EPA priority PAHs. Seasonal variation, diurnal patterns at two continuously monitored sites, and spatial gradients relative to identified emission sources were investigated. Positive matrix factorisation receptor modelling was applied for source apportionment, integrating elemental carbon, organic carbon, and metal markers. Cancer risk assessment using incremental lifetime cancer risk methodology was performed for population groups stratified by age and occupation. Results show significantly higher PAH concentrations during the dry harmattan season, with benzo(a)pyrene toxic equivalency concentrations at industrial-proximate sites exceeding WHO guidelines by factors of 3 to 8. Positive matrix factorisation identified four major source profiles: petroleum combustion, vehicular exhaust, biomass burning, and industrial process emissions, accounting respectively for 32, 28, 24, and 16 percent of total PAH mass. Cancer risk estimates for lifetime residents near flaring sites fell in the high-risk category. Findings provide actionable evidence for targeted emission reduction strategies in the Port Harcourt airshed. Keywords: polycyclic aromatic hydrocarbons, particulate matter, Port Harcourt, source apportionment, cancer risk