Typical haze events in Chengdu at the beginning of 2023 were investigated with bulk-chemical and single-particle analyses along with numerical model simulations. By integrating the obtained chemical composition, source, mixing state and numerical simulation results, we infer that Haze-1 was mainly caused by pollutants related to fossil fuel combustion, especially local mobile sources, while Haze-2 was triggered by the secondary pollutants, which mainly came from regional transmission.