Transport-Derived PM_2.5 and Black Carbon Aerosol Burden in West African Megacities: A Source-Attribution and Biofuel-Mitigation Case Study from Lagos, Port Harcourt, and Kano, Nigeria

Transport-related fine particulate matter (PM_2.5) and its black carbon (BC) component are a major, but atmospherically under-characterised, contributor to urban air quality degradation and short-lived climate forcing across sub-Saharan Africa. This study examines the PM_2.5/BC emission burden attributable to road transport fuel combustion and evaluates the atmospheric and climate co-benefits of a partial biofuel substitution in Lagos, Port Harcourt, and Kano, Nigeria's three busiest freight and commercial corridors.

A Tier-1 mass-balance emission inventory (IPCC/EMEP-EEA default emission factors, applied uniformly across all three cities in the absence of city-specific fleet data) was built from national fuel-sales activity data apportioned to the three cities by an assumed fuel-throughput share, and combined with Argonne GREET-derived life-cycle emission deltas for biodiesel-blend and bio-LNG pathways to estimate avoided emissions under defined heavy-duty fleet-switch scenarios. Published positive-matrix-factorisation (PMF) source-apportionment literature was used only for independent context and for a separate population-weighted mortality proxy, not to scale the emission-inventory totals.

All three cities exceed the WHO annual PM_2.5 guideline several-fold (4-14x); road transport accounts for approximately one-third of Lagos PM2.5 in PMF literature. The central 20%-heavy-duty-fleet, B20-blend scenario avoids an estimated 200 tonnes of diesel-related PM_2.5 per year (sensitivity range 110-280 tonnes from emission-factor uncertainty alone), rising to ~2,500 tonnes under an aspirational 100% neat-biodiesel conversion; SOx and well-to-wheel GHG/BC-relevant emissions fall proportionately. These are avoided-emission (tonnes/year) estimates; no dispersion modelling was performed, so ambient concentration-reduction (µg/m³) benefits are not yet quantified.

Nigeria's three-city transport corridor is a quantifiable, spatially concentrated aerosol and short-lived-climate-forcer source for which biofuel substitution offers a measurable emission-reduction lever, generalisable to comparable African transport corridors pending dispersion modelling and field validation of the activity-data and emission-factor assumptions used here.