Black carbon (BC) is an important component of particulate matter due to its effects on human health and climate. In this study, we present the first BC concentrations measured in the Istanbul megacity (similar to 15 million inhabitants). Two measurement campaigns have been conducted to measure BC and fine particulate matter (PM2.5) concentrations at four locations, characterized by different traffic densities. In the first campaign, BC daily mean concentrations have been found to be between 4 mu g/m(3) and 10 mu g/m(3). In the second campaign, BC and PM2.5 have been measured at the site with the highest traffic density for an entire year. Annually averaged BC contributes by 38 +/- 14% to the PM2.5 levels (annual average BC: 13 mu g/m(3) and PM2.5: 36 mu g/m(3)). Diurnal variations of BC concentrations followed those of traffic density (correlation coefficient of 0.87). These measurements are essential to identify the sources of BC and PM2.5 concentrations in Istanbul and develop mitigation measures. (C) 2013 Elsevier B.V. All rights reserved.