Chemical composition and mixing state of elemental carbon-containing particles from solid fuel combustion

Elemental carbon (EC), predominantly produced by solid fuel combustion, significantly influences both climate and public health. However, the physicochemical properties of EC-containing particles immediately after emission remain inadequately understood. This study investigates the chemical composition, size distribution, and mixing state of EC-containing particles from five solid fuels: wheat, corn, rice straw, bituminous coal, and anthracite. Using a single-particle aerosol mass spectrometer (SPAMS), we identified seven distinct EC-containing particle types. Our results show that biomass burning primarily produces EC-containing particles obviously coated with organic carbon (EC-OC) and organic nitrogen (EC-CN), with sizes concentrated between 0.4 and 1.0 μm. In contrast, bituminous coal emissions are dominated by sodium-rich EC-containing particles (EC-Na), while anthracite combustion predominantly produces particles coated with sulfate or nitrate (EC-NS). Bituminous coal particles are generally smaller (< 0.4 μm), likely due to higher volatile content and rapid pyrolysis. The mixing states of EC-containing particles varied markedly. Sulfate (⁹⁷HSO₄⁻) was strongly associated with EC-OC and EC-Na particles, resulting in a highly mixing state. Levoglucosan (⁵⁹C₂H₃O₂⁻) showed distinct patterns between biomass and coal emissions. These findings provide critical insights into the physicochemical properties of freshly emitted EC-containing aerosols, offering valuable references for atmospheric particle analysis and emission characterization.