Distance-decay Relationships of Air Pollutant Concentrations Near Open Waste Burning Sites in Nairobi, Kenya: Evidence from Kibera

Abstract

Open waste burning in informal settlements contributes to localized air pollution, posing significant health risks. This study investigated the distance-decay relationship of air pollutant concentrations near open waste burning sites in Kibera, Nairobi City County, Kenya. Air samples were collected at 21 sampling points across three distance ranges (0-500 m, 500-1000 m, and > 1000 m) from active burning sites over a two-month period in 2025. Pollutants measured included PM2.5, SO2, CO2, and CH4, using calibrated portable and fixed air quality monitors. Data were analyzed using linear regression and one-way ANOVA to examine relationships between pollutant concentrations and distance. PM2.5 levels were highest within 0-500 m, reaching 150 \(\mu\)g/m3 ten times the WHO 24-hour guideline of 15 \(\mu\)g/m3 and decreased to 45 \(\mu\)g/m3 beyond 1000m. SO2 exhibited a similar decline from 55ppb to 15ppb. Regression analysis indicated a significant negative relationship between distance and pollutant concentration (R2 = 0.530), while ANOVA confirmed differences across zones (F = 49.521, p<0.001). CO2 and CH4 showed more gradual declines but remained elevated near burning sites, highlighting greenhouse gas contributions. Pollutant concentrations declined sharply with distance from waste burning sites, with PM 2.5 and SO2  posing the highest immediate health risks. These findings support the establishment of buffer zones and targeted mitigation strategies in Nairobi’s informal settlements to protect public health.