We investigated changes in sources of carbonaceous aerosol and their effect on long-term trends in elemental carbon (EC) and organic carbon (OC) concentrations at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) in Okinawa, Japan, for the period 2004-2013. EC and OC concentrations were measured by using a semi-real-time carbon monitor and performing an offline filter analysis involving the thermal-optical method, following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol.Overall, the annual average concentration of EC did not change between 2004 and 2013, whereas the OC concentration clearly decreased at the rate of 0.11 μg C m −3 yr −1 (α > 0.05).