Assessment of the Contribution of Road Traffic Emissions to Urban Air Pollution in Lagos Island

Road traffic is the dominant source of urban air pollution in Lagos, Nigeria's commercial capital, where vehicle fleet age, traffic congestion, and fuel quality combine to generate substantial emissions of pollutants affecting human health and the urban environment. This study assesses the contribution of road traffic emissions to urban air quality degradation on Lagos Island, focusing on carbon monoxide, nitrogen dioxide, and fine particulate matter concentrations. Ambient air quality was measured at twelve roadside and six background monitoring sites using portable electrochemical and optical particle sensors deployed during peak and off-peak traffic periods across eight weeks in 2024. Vehicle count surveys were conducted simultaneously to characterise traffic volume and fleet composition. Receptor modelling using principal component analysis identified traffic-related emission signatures in the air quality dataset. Findings indicate that roadside carbon monoxide concentrations during morning peak hours reach 18 to 24 parts per million, exceeding World Health Organisation guidelines by a factor of six to eight. Traffic-related emissions account for approximately 71 percent of the variance in roadside PM2.5 concentrations at the sampled sites. Older diesel-powered commercial vehicles operating on major arterial roads are identified as disproportionately high emission contributors. The study recommends vehicle emission testing programme enforcement, promotion of cleaner cooking and transport fuel substitutes, and establishment of low-emission zones around schools and hospitals on Lagos Island. Keywords: road traffic emissions, air pollution, Lagos Island, particulate matter, urban air quality.