Spatio-Temporal Variation of PM-bound Heavy Metals Along a Major Motorway in Ibadan, Nigeria

Traffic-related particulate matter (PM ) contributes extensively to 10 ambient air pollution and are reported to be associated with respiratory illnesses. Populations living along major urban motorways are at higher risk. This study evaluated levels of PM bound heavy metals along Idi 10 Ape – Iwo busy motorway in Ibadan. Five sampling locations 150 metres apart were purposively selected along the road, namely: Abayomi Area (AA), Iyana Agbala (IA), Barracks Area (BA), Agbaakin Layout (AL) and Holiness Junction (HJ). Air samples were collected at each location at peak periods (7-10am and 1-4pm) for 10 weeks. Traffic density was estimated via manual counting. Filters were digested using standard methods and extracts were analysed for Pb, Fe, Cu, Cd, Zn, Cr and Ni using atomic absorption spectrophotometry technique. Mean traffic density for all locations and vehicles ranged from 992 – 21149. Daily mean PM for all sampling locations ranged 10 3 from 84.6±41.7 – 122±60µg/m , with levels at least three times higher 3 than WHO guideline limit of 20µg/m . Mean metal concentrations 3 (mg/m ) for all locations were: Pb- 279±149, Fe-2.20±1.97, Cu – 0.0178±0.0090, Cd – 138±37, Zn – 0.428±0.196 and Cr – 0.179±0.06 2 7 with levels higher in order 10 – 10 in magnitude. This suggests a hazardous PM . There was no regular trends in all parameters in time 10 and space within the study period. Mean metal concentrations increased proportionally with traffic density for all sampling locations. Policies on traffic-related pollution become pertinent to reduce these slow killing pollutants associated with dust and exhaust fumes from motorways in Nigeria