High airborne black carbon concentrations measured near roadways in Nairobi, Kenya

•Nairobi’s street-side workers are exposed to unhealthy levels of black carbon (BC).•High concentrations of BC suggest elevated risk of cancer in Nairobi from diesel emissions.•A simple reflectance method for Teflon filters can estimate BC levels in Nairobi.•Policy makers should prioritize mitigation of poor air quality in Nairobi.•Poor air quality inhibits sustainable economic development.