Effect of oxygen concentration on PM_2.5 formation during coal combustion under O₂/CO₂ atmosphere

Pulverized coals were burned in a tube furnace under O₂/CO₂ atmosphere, and an electrical low pressure-impactor (ELPI) was used to collect the PM_2.5. The results show that a bimodal distribution of PM_2.5 appears, which is located at 0.1 μm and 2.0 μm, respectively. The mass concentrations of PM_2.5 increase with5 enhancing the O₂ concentraion. The enrichment of S, Na and K on the sub-micron particles is observed, but that of Si and Ca is not observed. It is proposed that sub-micron particles are formed via the mechanism of vaporization and condensation, and the super-micron particles are formed by the fragmentation of coal char and the coalescence of inherent mineral matter based on the analyses of particle size distribution, elements distribution and morphology of PM_2.5.