Emission characteristics and cytotoxic effects of PM_2.5 from residential semi-coke briquette combustion

Coal combustion emits large amounts of PM_2.5 (particulate matter with a diameter of ≤ 2.5 μm), and the emissions from different coal types differ. Clean fuels are essential in reducing PM_2.5 emissions and their respiratory effects on human. This study compared PM_2.5 emissions and their chemical components from four types of coal (i.e., bituminous raw-coal chunk, semi-coke briquette, anthracite, and bituminous briquette). The bioreactivies triggered by PM_2.5 exposure to human alveolar epithelial (A549) cells were compared, and the emission factors (EFs) of bioreactivies were calculated. The PM_2.5 EFs of semi-coke briquettes were reduced efficiently compared with those of raw-coal chunk, and their chemical profiles also differed. The contribution of total carbon and metals (i.e., S, Cl, Zn, and Pb) was higher for semi-coke briquette relative to raw-coal chunk, which may be due to the concentration effect of the semi-coke briquette preparation process. The production of lactate dehydrogenase (LDH) and reactive oxygen species (ROS) was higher for semi-coke briquette relative to raw-coal chunk at the PM_2.5 exposure dose of 100 μg mL⁻¹. The EFs of LDH and ROS for semi-coke briquette, anthracite, and bituminous briquette were substantially lower than those for raw-coal chunk, which verified the effects of clean coal on oxidative stress and cytotoxicity. Organic carbon and specific heavy metals (i.e., Cu, Fe, Ni, Zn, Pb, and Cr) were significantly correlated with cell membrane damage and oxidative stress. This study clarifies potential adverse effects of PM_2.5 emissions from the combustion of various coal types and highlights the necessity of adopting clean coal to reduce PM_2.5 emissions and cytotoxicity.