Theoretical and Empirical Contributions to Understanding the Health Effects of Seasonal Harmattan Haze on Vulnerable Populations in North West Nigeria

The harmattan season in North West Nigeria generates extreme ambient dust conditions from Saharan dust transport, with seasonal PM10 and PM2.5 concentrations frequently exceeding national and international air quality guidelines by orders of magnitude, yet the health burden attributable specifically to harmattan haze exposure in this region has not been rigorously quantified through original epidemiological research. This dissertation develops an original theoretical model of harmattan-health vulnerability interactions and tests it empirically through a two-year prospective study in Kano, Sokoto, and Kebbi states, North West Nigeria. The theoretical model integrates atmospheric transport modeling, human exposure science, host susceptibility frameworks, and social vulnerability theory. Ambient PM2.5 and PM10 were continuously monitored at twelve stations from October to March across two harmattan seasons. Personal exposure monitoring was conducted on 120 participants stratified by age, sex, occupational exposure, and pre-existing respiratory condition status. Weekly health outcome assessments included spirometry, blood pressure, peak expiratory flow measurement, and respiratory and cardiovascular symptom diaries. Time-series analysis using distributed lag non-linear models estimated exposure-response relationships with a twenty-one day lag structure. Results showed that a 10-microgram-per-cubic-metre increase in twenty-four-hour PM2.5 was associated with a 3.2 percent increase in respiratory hospital admissions and a 1.8 percent increase in cardiovascular emergency visits. Children under five and adults over sixty years demonstrated the greatest vulnerability. The dissertation makes an original contribution to the epidemiological characterization of harmattan health impacts and provides exposure-response data for Nigerian air quality standard revision. Keywords: harmattan, PM2.5, North West Nigeria, health vulnerability, air quality.