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Rapid urbanization, industrial development, and population growth in East Africa are driving a decline in air quality, with fine particulate matter (PM2.5) posing significant health risks. The region's complex topography interacts with local microclimates, influencing pollutant dispersion and accumulation, yet these combined effects remain poorly understood. This chapter investigates PM2.5 pollution in relation to microclimate dynamics in Kigali, Rwanda, from 2019 to 2024, using bias-corrected surface total PM2.5 mass concentration (MERRA2_CNN_HAQAST), ERA5 planetary boundary layer height (PBLH), and NASA Prediction of Worldwide Energy Resources data for temperature, relative humidity, wind speed, and precipitation. This chapter aimed to link PM2.5 variability to microclimate processes, aligning with the book’s theme of Microclimate Monitoring, Mitigation, and Adaptation in Deltas, and providing insights to support effective air quality mitigation and adaptation in rapidly urbanizing regions. Hourly PM2.5 ranged from 1.30 to 95.05 µg/m3 (mean = 29.05 ± 11.96 µg/m3), with seasonal peaks in the long dry season (June–August, 34.02 µg/m3) and minima in the long wet season (March–May, 23.10 µg/m3). The annual mean PM2.5 (25–30 µg/m3) far exceeded the 2021-WHO guideline of 5 µg/m3, indicating chronic exposure risks. Hourly observations showed that the average temperature was 19.66 ± 3.86 °C, humidity was 77.61 ± 18.05%, wind speed was 2.20 ± 1.06 m/s, and the PBLH was 484.65 ± 521.65 m. Interannual analysis revealed PM2.5 fluctuations associated with microclimate variabilities: in 2021, PM2.5 rose by 0.61 µg/m3 with temperature, humidity, wind speed, and PBLH changing by − 0.06 °C, − 0.74%, + 0.06 m/s, and + 16.78 m; in 2023, PM2.5 fell by 4.27 µg/m3 with + 1.21 °C, − 4.81%, + 0.14 m/s, and + 6.04 m; and in 2024, PM2.5 decreased by 0.60 µg/m3 with + 0.46 °C, − 0.87%, − 0.17 m/s, and + 9.76 m, respectively. PM2.5 exhibits a moderate negative correlation with temperature, wind speed, and PBLH (r ≈ − 0.36 to − 0.39), and a positive correlation with humidity (r = 0.27), indicating accumulation in shallow and humid layers. This chapter highlights the key drivers of PM2.5 in a data-scarce region and offers a microclimate-sensitive framework for emission reduction, urban planning, and climate adaptation. These insights are applicable to similar environmental settings globally.

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Monitoring Microclimate Impacts on PM2.5 Pollution in the Densely Populated and Topographically Complex Cities of East Africa: A Case Study of Kigali, Rwanda

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  • 发表日期：

    2026年

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  • Irankunda Elisephane

摘要

Rapid urbanization, industrial development, and population growth in East Africa are driving a decline in air quality, with fine particulate matter (PM2.5) posing significant health risks. The region's complex topography interacts with local microclimates, influencing pollutant dispersion and accumulation, yet these combined effects remain poorly understood. This chapter investigates PM2.5 pollution in relation to microclimate dynamics in Kigali, Rwanda, from 2019 to 2024, using bias-corrected surface total PM2.5 mass concentration (MERRA2_CNN_HAQAST), ERA5 planetary boundary layer height (PBLH), and NASA Prediction of Worldwide Energy Resources data for temperature, relative humidity, wind speed, and precipitation. This chapter aimed to link PM2.5 variability to microclimate processes, aligning with the book’s theme of Microclimate Monitoring, Mitigation, and Adaptation in Deltas, and providing insights to support effective air quality mitigation and adaptation in rapidly urbanizing regions. Hourly PM2.5 ranged from 1.30 to 95.05 µg/m3 (mean = 29.05 ± 11.96 µg/m3), with seasonal peaks in the long dry season (June–August, 34.02 µg/m3) and minima in the long wet season (March–May, 23.10 µg/m3). The annual mean PM2.5 (25–30 µg/m3) far exceeded the 2021-WHO guideline of 5 µg/m3, indicating chronic exposure risks. Hourly observations showed that the average temperature was 19.66 ± 3.86 °C, humidity was 77.61 ± 18.05%, wind speed was 2.20 ± 1.06 m/s, and the PBLH was 484.65 ± 521.65 m. Interannual analysis revealed PM2.5 fluctuations associated with microclimate variabilities: in 2021, PM2.5 rose by 0.61 µg/m3 with temperature, humidity, wind speed, and PBLH changing by − 0.06 °C, − 0.74%, + 0.06 m/s, and + 16.78 m; in 2023, PM2.5 fell by 4.27 µg/m3 with + 1.21 °C, − 4.81%, + 0.14 m/s, and + 6.04 m; and in 2024, PM2.5 decreased by 0.60 µg/m3 with + 0.46 °C, − 0.87%, − 0.17 m/s, and + 9.76 m, respectively. PM2.5 exhibits a moderate negative correlation with temperature, wind speed, and PBLH (r ≈ − 0.36 to − 0.39), and a positive correlation with humidity (r = 0.27), indicating accumulation in shallow and humid layers. This chapter highlights the key drivers of PM2.5 in a data-scarce region and offers a microclimate-sensitive framework for emission reduction, urban planning, and climate adaptation. These insights are applicable to similar environmental settings globally.