a b s t r a c tBlack carbon (BC) and tropospheric ozone (O 3 ) are two main short-lived climate pollutants also linked to health effects. They are ubiquitous in street canyons, since this environment is a hotspot for trafficrelated pollutants due to their particular airflow characteristics, location within the cities and the high density of vehicles and population.We report on BC and O 3 concentrations measured in a Brazilian city in November 2014. Measurements of BC at 880 nm wavelength were conducted in a street canyon on the north and south façades and at rooftop level (7 wavelengths, including 880 nm) whereas O 3 was recorded only on the south façade. Concurrent meteorological data were gathered at a suburban and a rooftop sites.Clear diurnal patterns were found for BC related to traffic emissions and atmospheric mixing conditions. Ozone peaked in the afternoon in response to maximum photochemical production and at night most likely linked to vertical and/or horizontal transport. By using conditional bivariate probability functions, we identified on-road traffic as the main local source for BC during daytime, and at night an intermittent signal was associated with local waste and biomass burned on the city's outskirts. A complementary air backward trajectory analysis helped conclude that locally produced O 3 was enhanced by regional transport from large cities and/or biomass smoke.Mitigation strategies for BC and O 3 depletion should target the vehicle fleet, particularly diesel buses, reduction of biomass and waste burning at local level, and decrease of open biomass burning in large areas in Brazil and neighbor countries.