PM_(2.5) in Abuja, Nigeria: Chemical characterization, source apportionment, temporal variations, transport pathways and the health risks assessment

摘要

Due to rapid industrial development and urbanization, Abuja is characterized with poor and deteriorated air quality. The level of PM(2.5 )concentrations in Abuja is very high and above the statutory limits; however, the high levels of pollution in Lugbe do not seem to be consistent with local emission sources. This study analyzed the chemical composition of PM2.5 to perform source identification and contributions in Lugbe, Abuja, Nigeria. Sampling in 2016 provided 246 PM2.5 samples at 2 sites across all the four months of sampling. The highest ambient PM2.5 concentration (142 pg m(-3)) was recorded in winter while the lowest (84 pg m -3 ) was observed in summer. Chemical mass closure suggested that dust (40.5%) contributed most of the PM2.5 mass. Source apportionment of PM2.5 was performed using positive matrix factorization (PMF) model and six sources were identified. They include mineral dust, crustal dust, vehicle exhaust, secondary nitrate, secondary sulfate, and industrial sources. Crustal dust, vehicle exhaust, and secondary sulfate were the major sources of ambient PM2.5 in Lugbe, contributing 33.3, 29.8, and 18.0%, respectively. The results of 120-h backward trajectories showed that external northeastern region was more dominant in January, while during the remaining three months, southwesterly winds prevailed. The results of bivariate polar plots for most of the factors showed the influence of the southern areas of Lugbe. The study found that there was long-range regional transport of PM2.5 into Lugbe area throughout the four months. Risk assessments revealed that ingestion route was the major exposure pathway for both children and adults. Non-carcinogenic and carcinogenic risk levels were below the acceptable threshold limits. Finally, the results of this study have shown that ambient air quality in Lugbe can be substantially improved by reducing the emissions from crustal dust, vehicle exhaust, and secondary sulfate sources in the external southern regions.