Physicochemical Properties and Toxicity of Coal Combustion emission with Photochemical Aging process

Abstract

Coal is a significant source of fine particulate matter emissions due to its widespread use and abundant global reserves. It has the highest disease burden among fossil fuels. As the second most consumed primary energy source worldwide, coal is used both commercially (87%) and residentially (3%). However, residential coal combustion results in a higher proportion of premature deaths (34%) compared to commercial use (16.2%). Incomplete combustion in simple devices leads to significant emissions that degrade air quality and affect health. Coal types include anthracite, bituminous, sub-bituminous, and lignite, with bituminous coal being the most versatile and widely used for residential heating and cooking. Residential combustion, occurring at 396-550°C, often leads to incomplete combustion and the release of gases and particulate matter. These emissions can undergo long-range transport and atmospheric aging, altering their chemical composition and toxicity. This study aimed to observe how the changes in the physicochemical properties of particulate matter from low-temperature coal combustion before and after aging affect their biological toxicity. A laboratory-scale coal combustion system was used, and crushed coal (<75 μm) was combusted at 550℃. The particles generated through the coal combustion system were aged for 1.1 days using a potential aerosol mass-oxidation flow reactor (PAM-OFR) connected to the chamber downstream. The chemical components of the collected particles (ions, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and elements) were analyzed, and oxidative potential (OP) was measured using the dithiothreitol (DTT) assay. In the aged coal combustion particles, the mass concentration of all ions increased compared to the pre-aged particles, with significant increases in NH4+ and SO42- ions. Furthermore, the WSOC/OC ratio, an indicator of secondary organic aerosol (SOA) formation, significantly increased after aging. The oxidative potential was higher in the pre-aged samples. Biological toxicity was measured using the Neutral Red Uptake assay (NRU) for cytotoxicity, ELISA for inflammatory response, DCFH-DA for oxidative stress, and Comet assay for DNA damage. The pre-aged samples showed higher values for oxidative stress and DNA damage indicators compared to the aged samples, whereas the aged samples exhibited higher values for cytotoxicity and inflammatory response than the pre-aged samples.