Assessment of the effects of urbanization-induced air pollution on human respiratory health in Rwanda

Abstract

Urbanization-driven land use changes and urban activities contribute to environmental degradation, intensify climate change, and pose growing risks to public health. This thesis aimed to investigate the impact of urbanization-induced air pollution on respiratory health in Rwanda. Using Landsat satellite imagery and GIS tools, changes in Land Use and Land Cover (LULC) and associated urban indices from 1990 to 2020 were mapped for Kigali. The modified Mann-Kendall test and Sen’s slope estimator were applied to assess trends in air temperatures. Built-up areas increased at an average rate of 3.39 km²/year, while open lands declined by 5.81 km²/year. Simultaneously, air temperature showed significant upward trends, with minimum temperatures increasing by 0.51 °C per decade during the long dry season (JJA) and maximum temperatures increasing by 0.49 °C per decade in the short dry season (JF). Strong positive correlations (r > 0.61, p ≤ 0.05) were observed between air temperature and urban indices across all subregions. To evaluate the degree of personal exposure to air pollution, PM2.5 levels were monitored among 150 participants engaged in seven major urban activities across five rapidly growing cities of Rwanda over five consecutive days in dry season. PM2.5 concentrations in work microenvironments ranged from 12.67 μg/m³ to 192.64 μg/m³, higher than those recorded at home (11.69 to 72.54 μg/m³) and other microenvironments (13.25 µg/m3 to 113.58 µg/m3). Exposure contributions and personalambient differences were dominated by the work microenvironment, with some participants exposed to maximum PM2.5 concentrations up to 22 times higher than ambient levels. These findings indicate the significant effects of daily personal activities and visited microenvironments on personal exposure, and the importance of considering a personal lifestyle in understanding the true personal exposure. To investigate the interactive effects of temperature and ambient air pollution with a focus on differences in urbanization levels on hospital visits for Chronic obstructive pulmonary disease (COPD) and Acute Respiratory Infections (ARIs) over Rwanda, the sector territories were used and categorized into municipalities and agglomerations. Principal component multivariate analysis was applied to generate urban, temperature, and air quality indices, while correlation analysis was used to evaluate their respective relationships with health parameters. Results showed that municipalities recorded higher ambient pollution levels compared to agglomerations. These levels were associated with increased hospital visit rates for respiratory diseases, with correlation coefficients reaching up to ρ = 0.776 and τ = 0.584 for COPD, and ρ = vi 0.672 and τ = 0.494 for ARIs between respiratory disease incidences and air quality index. On the other hand, significant positive correlations were observed between urban index and ARIs in all sectors (ρ = 0.518; τ = 0.366) but the prevalence of respiratory diseases was more closely linked to air quality rather than simply the population size or density in municipalities. The findings of this thesis are valuable for assessing environmental challenges related to land use and for developing long-term strategies to mitigate its impacts on respiratory health.