Abstract PM 2.5 is associated with multiple adverse health outcomes, yet data on its concentration, composition and sources in African cities remain limited. This study presents the first detailed characterisation of outdoor PM 2.5 in Johannesburg, South Africa. Twenty-four-hour filter samples were collected every sixth day from 3 October 2020 to 12 October 2021 at a residential site in the suburb of Buccleuch. Samples were analysed using gravimetric methods, smoke-stain reflectometry, optical t