Exposure Assessment of Commuters to Traffic - Related Air Pollutants in Transportation Micro-Environments of Developing City of Port Harcourt, Rivers State, Nigeria

Abstract

Urban transportation micro-environments are recognized as critical exposure hotspots for traffic-related air pollutants, yet they are often underrepresented in conventional ambient air quality assessments. This study investigated the exposure of commuters to particulate matter (PM₁.₀, PM₂.₅, PM₁₀), water-soluble ions, trace metals (Pb, Cd, Cr, Ni, Cu, Zn), and polycyclic aromatic hydrocarbons (PAHs) in selected transportation micro-environments of Port Harcourt, Rivers State, Nigeria. Sampling was conducted across public buses, commercial motorcycles, and roadside bus stops in the Aluu and Isiokpo communities, representing high-density commuter zones. Samples were collected over a 10-day period in both dry and wet seasons using standardized air monitoring protocols. Analytical procedures included gravimetric PM determination, ion chromatography for water-soluble ions, atomic absorption spectroscopy for trace metals, and gas chromatography-mass spectrometry for PAHs. Results indicate that commuters are consistently exposed to moderate levels of air pollutants, with PM₁.₀ concentrations ranging from 44.1 to 52.7 µg/m³, PM₂.₅ from 69.0 to 78.1 µg/m³, and PM₁₀ from 102.2 to 110.8 µg/m³. Water-soluble ions, including sulfate, nitrate, ammonium, and chloride, were detected at moderate concentrations, reflecting both primary vehicular emissions and secondary atmospheric formation processes. Trace metals and PAHs, including carcinogenic benzo[a]pyrene, were present at levels indicating moderate contamination, with commercial motorcycles exhibiting slightly higher concentrations than buses or bus stops due to proximity to exhaust emissions and stop-andgo traffic dynamics. Seasonal variations influenced pollutant levels, with higher concentrations recorded during the dry season, primarily due to increased dust resuspension and reduced precipitation. Correlation analysis revealed strong associations between EC and PAHs, confirming that carbonaceous particles act as carriers for toxic organic compounds, while significant correlations between PM₁.₀ and trace metals highlight the role of fine particles as vectors for metals in commuter microenvironments. The cumulative exposure observed, although classified as moderate, poses potential long-term health risks, including respiratory irritation, cardiovascular effects, and carcinogenic outcomes from prolonged inhalation of PAH-laden particulate matter. The study underscores the importance of transportation microenvironments as critical hot-spots for urban air pollution exposure and emphasizes the need for targeted mitigation strategies, including adoption of cleaner fuels, improved vehicle maintenance, deployment of emission control technologies, urban planning measures to reduce congestion, and public awareness campaigns to reduce exposure. These findings provide essential data for policymakers, urban planners, and public health authorities in Port Harcourt and similar developing cities, offering an evidence-based framework to minimize commuter exposure and improve urban air quality