In this work, the effects of different torrefaction temperatures and durations on the physicochemical properties of rice straw (RS), and the emission characteristic of PM10 (particulate matter with aerodynamic diameters of <= 10 mu m) during torrefied RS combustion, were investigated. Results indicate that the release of Cl and K, and decomposition of the organic matrix demonstrated a promoting effect during torrefaction. However, the removal of Cl and K did not reduce the emission of PM1. The emission concentration of PM1 and PM1-10 generated from torrefied RS was enhanced, and the yields of PM1-10 was much higher than those of PM1. The concentrations of K and Cl in PM1-10 increased with torrefaction temperature, combined with the microstructure, indicating that the torrefaction pretreatment promoted the heterogeneous condensation of KCl vapour to form PM1-10.