Seasonal variation and health risk of atmospheric nitrogen dioxide in Ondo state, Nigeria

Nitrogen dioxide (NO₂) has been identified as a significant contributor to respiratory issues, including childhood asthma, and is closely linked to climate change and global warming. This study measured atmospheric NO₂ concentrations at five locations across Ondo State, Nigeria, using a portable NM-4 multi-gas detector. Sampling sites were purposively selected across industrial, high-traffic (busy road), and residential areas based on potential NO₂ emissions. The mean NO₂ concentrations (in ppm) recorded were 1.85 ± 0.47 during the wet season and 2.96 ± 0.46 in the dry season. The study also evaluated the potential health risks associated with NO₂ exposure using hazard quotient (HQ) and total hazard quotient (THQ) assessments. For adults, the THQ ranged from 5.40 × 10⁻⁷ to 8.50 × 10⁻⁷, and for children, from 5.90 × 10⁻⁷ to 9.40 × 10⁻⁷. HQ values indicated elevated health risks (HQ > 1), particularly among children, with ranges from 1.29 to 2.05, while adults had values from 4.71 to 7.48. The ranking of exposure risk across sites was D > B = C > E > A for adults and D > B > C > E > A for children. These findings reveal that ambient NO₂ levels in the study areas pose significant health threats, especially exceeding the safety thresholds established by the United States Environmental Protection Agency (USEPA). The results underscore the urgent need for targeted air quality monitoring, emission control policies, and public health interventions in rapidly urbanizing regions of Nigeria and similar low-resource settings where regulatory frameworks remain underdeveloped.