Spatio-temporal assessment of classroom air quality and thermal comfort as determinants of respiratory health risks in urban pre-tertiary institutions.

Poor indoor environmental quality (IEQ) remains a significant driver of paediatric morbidity, yet data on the interplay between particulate matter (PM), building design, and health in tropical schools are sparse-a gap exacerbated by severe data scarcity and policy deficits across sub-Saharan countries. In this study, the spatio-temporal dynamics of classroom air quality and thermal comfort were investigated to identify the key environmental determinants of respiratory health risks among primary and secondary school students in Benin City, Nigeria. A mixed-methods approach combining objective environmental monitoring and subjective assessments was deployed across six schools for 10 weeks. IEQ parameters (PM2.5, PM10, CO, and CO2) and thermal indices were monitored, while health data were collected through modified British Medical Research (BMR) questionnaires and analysed using descriptive, inferential, and multivariate logistic regression. To estimate non-carcinogenic health risks, the hazard quotient (HQ) was calculated using the US States Environmental Protection Agency (US EPA) framework. The PM2.5 and PM10 concentrations ranged from 11.2 to 81.4 µg/m3 and 20.1 to 138.6 µg/m3, respectively. The CO2 concentration peaked at 729.3 ± 28.4 ppm, while high temperature‒humidity index (THI) values (28.3-30.1) indicated severe heat discomfort. Health risk assessment revealed that all HQ values for PM2.5 and PM10 remained below unity (HQ < 1), suggesting that students were not at immediate risk of chronic non-carcinogenic effects; however, the high prevalence of reported respiratory symptoms-including coughing (58.2%), phlegm (32.5%), and chest pain (26.7%)-underscores that acute respiratory irritations frequently manifested well below these chronic regulatory thresholds. Multivariate analysis revealed that elevated PM exposure was strongly associated with an increased risk of coughing (p < 0.001) and significantly increased the odds of chest pain (crude OR = 2.74; p = 0.001). Poor sanitation was the strongest predictor of phlegm production (AOR = 5.54; 95% CI 1.35-22.80; p = 0.018) after adjustment for confounders, including age, sex, and socio-economic status. This study highlights a critical link between the school-built environment and student respiratory health. While chronic risk thresholds (HQs) were not exceeded, particulate matter and sanitation emerged as the primary drivers of acute respiratory symptoms, demonstrating that immediate health risks persist within poorly regulated tropical academic environments.