Patterns and drivers of maternal personal exposure to PM2.5 in informal settlements in Nairobi, Kenya†

There is limited data on personal exposure to fine particulate matter (PM_2.5) for mothers in informal settlements in Africa. Identifying and characterizing the sources of exposure to PM_2.5 for this population is key to finding potential solutions for mitigating air pollution exposures. As part of the USAID-funded Kuboresha Afya Mitaani Urban Maternal, Newborn and Child Health project in Nairobi, Kenya, this study aimed to (1) characterize and map environments that contribute to fine particulate matter (PM_2.5) exposure for mothers and infants and (2) determine which factors drive exposure to PM_2.5. Mothers were enrolled and measured for 24 hours with PM_2.5 monitors and GPS loggers in two informal settlements in Nairobi (Dagoretti and Starehe), with complete data received from 73 participants. Two ambient PM_2.5 monitors were also installed in each of the respective communities. Time-activity surveys were administered following the monitoring period. Mean daily exposures were 39.9 and 45.5 µg m⁻³ in Dagoretti and Starehe, respectively, with 60% of samples exceeding the annual WHO Annual Interim-1 Target of 35 µg m⁻³. Normal daily activities such as sleeping, resting, running errands, and visiting with friends constituted over three-quarters of exposure sampling time. These activities were not associated with elevated PM_2.5 exposures, and generally tracked diurnal ambient patterns (morning and evening peaks). Personal exposures, however, did peak higher than ambient in the evenings when cooking was most common, and cooking with wood or charcoal was associated with higher PM_2.5 personal exposures (daily mean of 54.2 µg m⁻³ [n = 16], compared to 40.3 µg m⁻³ for those who used gas, liquid fuels or electricity [n = 57]). These results suggest that transitioning households to cleaner fuels, such as electricity, LPG, or ethanol, would be the most promising intervention that could rapidly reduce exposures of mothers in informal settlements where biomass use is common. At the same time, larger-scale sectoral efforts are needed to bring ambient PM_2.5 concentrations, and thus the overall population exposures, closer to WHO guidelines.