A source-oriented version of the CMAQ model was used to quantify contributions from nine regions to PM_2.5 and its components in the 18 cities within Sichuan Basin. Nonlocal emissions contribute 39–66 % and 25–52 % to the citywide average PM_2.5 concentrations of 45–126 and 14–31 µg m³ in the winter and summer, respectively. This study demonstrates the importance of joint emission control efforts among cities within the SCB and neighboring regions to the east.