On-road vehicular traffic emissions inventory and air quality on major roadways in Lagos City

Traffic-related air pollution (TRAP) is a serious public health risk in today's cities, causing premature death and a wide range of global diseases such as respiratory, cardiovascular, and neurological disorders. This study evaluated a local emission inventory and monitored ambient air quality in the Lagos metropolis through roadside observations of five traffic air pollutants using portable emission devices on selected roadways. Traffic mobility metrics, such as flow, speed, and vehicle fleet composition, were recorded over eleven (11) hours daily. Geospatial analysis identified pollution hotspots across various emission monitoring points on each corridor. Findings revealed that arterial composition and traffic flow significantly influence emission levels. The highest traffic volumes were recorded during the morning (7–9 a.m.) and evening (4–8 p.m.) peak periods, while the lowest pollutant concentrations occurred during the afternoon (12–2 p.m.). Pollutant levels were notably higher at bottlenecks near intersections or in traffic jams compared to points farther from the road corridors. SO₂ and NO₂ concentrations indicated moderate pollution across all routes. However, CO, PM₂.₅, and PM₁₀ concentrations on commercial and industrial routes posed severe health risks, rendering the air quality unsafe to health. Enhancing air quality monitoring across Sub-Saharan Africa (SSA) is essential for developing robust national responses to combat air pollution and safeguard public health.