Seasonal variability and human health risk assessment of airborne particulate matter in Ibadan Metropolis, Nigeria

Abstract

Air pollution, particularly fine particulate matter PM2.5, poses significant public health risks in rapidly urbanizing cities of Sub-Saharan Africa. This study evaluates seasonal variability and non-carcinogenic human health risks associated with ambient PM2.5 and PM10 in Ibadan Metropolis, Nigeria, using high-resolution one-hour averaged data from a calibrated PurpleAir sensor deployed at the National Space Research and Development Agency NASRDA Ibadan Zonal Office between March 2021 and October 2022. Monthly mean PM2.5 concentrations ranged from 32.0 to 155.5 µg/m3, while PM10 ranged from 34.1 to 174.2 µg/m3, consistently exceeding the 2021 World Health Organization annual guideline for PM2.5 (5 µg/m3). Pronounced dry-season (November–March) elevations, particularly during Harmattan months, were observed. Air Quality Index analysis identified PM2.5 as the dominant pollutant, with values exceeding 300, corresponding to the Hazardous category during peak dry-season episodes. Hazard Index values exceeded unity throughout the study period, peaking close to 10 for infants in March 2021, indicating substantial non-carcinogenic risk associated with reduced lung function and increased hospitalization. Age-stratified analysis revealed increasing vulnerability with decreasing age, with infants most at risk, followed by children and adults. These findings represent the first age-stratified non-carcinogenic risk assessment in Ibadan using continuous sensor data and the first application of the Air Quality Life Index in a Nigerian urban context. They also inform policy in other tropical savanna cities facing similar motorization-dust synergies, such as Accra, Ouagadougou, and Bamako.