Section 2.6 of the “State of the Climate in Kenya 2025” report, which includes contributions from SEI researchers, analyses the status of air pollution in Nairobi, focusing on fine particulate matter (PM2.5). These aerosols, which are 2.5 micrometers or smaller in diameter, often consist of smoke, soot, liquids or solid particles, or biological matter like mould, bacteria, and pollen. PM2.5 can penetrate deep into the lungs and enter the bloodstream, causing serious health issues such as respiratory diseases, cardiovascular problems, and premature death.

The analysis evaluates yearly averages of PM2.5 levels for 2024 and 2025, allowing for a comparison of pollution between years and locations, and highlighting spatial exposure patterns in the city.

Key findings:

• The concentration of PM2.5 was within the Kenyan national air quality standard of 35 μg/m³ per year but exceeded the World Health Organization (WHO) air quality guidelines of 5 μg/m³, thus exposing populations to health risks.
• The highest PM2.5 concentrations were recorded at monitoring sites located in densely populated residential areas in Nairobi, including Dandora Phase 4, Kariobangi Health Center, and Nyayo Estate Gate B. Air pollution in these areas was likely caused by emissions from traffic, informal burning of waste, small-scale industrial activities, and fuel combustion from households.