Impact of Coal Mining on Air Quality in Okaba, Ankpa Local Government Area, Kogi State, Nigeria: Assessment, Health Index, and Policy Implications

Coal mining is a critical economic activity in Okaba, Ankpa Local Government Area of Kogi State, Nigeria, but its environmental and public health consequences have remained inadequately quantified. This study investigated the impact of coal mining on ambient air quality at nine purposively selected coal mining sites (Sites A–I) in Okaba, measuring four key air pollutants — particulate matter (PM2.5 and PM10), carbon monoxide (CO), and nitrogen oxides (NOx) — across three daily measurement intervals (07:00–09:00, 12:00–14:00, and 17:00–19:00 hours) during both the wet season (April–August) and dry season (November–March). A portable Precision Digital Air Quality Detector (HB-90A) and a polludrone machine were deployed at 1.5 metres above ground level. Air quality data (n = 216 measurements) were analysed using descriptive statistics and one-way Analysis of Variance (ANOVA). A standardised air quality health index (AQHI) was also developed using WHO breakpoint interpolation to assess population health risk. Results revealed that PM2.5 concentrations peaked at 38 μg/m³ in the evening and 37 μg/m³ at Site F during the dry season, both substantially exceeding the WHO 2021 24-hour guideline of 15 μg/m³. All nine sites exceeded WHO PM2.5 standards, eight of nine exceeded PM10 and CO limits, and Site H exceeded NOx limits. ANOVA confirmed no statistically significant diurnal variation (p = 1.16E-69) or cross-site variation (p = 1.12E-22), and no significant seasonal difference in overall air quality (p = 0.935). The AQHI revealed that 20.4% of coal mining sites exhibited 'Unhealthy' air quality conditions, posing significant respiratory risks to miners and surrounding communities. These findings underscore the urgent need for regulatory enforcement, environmental monitoring, buffer zone policy, and occupational health interventions in Nigeria's coal mining sector.

Coal mining; air quality; particulate matter; PM2.5; PM10; carbon monoxide

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