Physicochemical properties and oxidative potential of fine particles produced from coal combustion

The physical and chemical properties as well as the oxidative potential (OP) of water soluble components of coal combustion fine particles were examined. A laboratory-scale pulverized-coal burning system was used to produce coal combustion particles at different burning temperatures of 550 °C, 700 °C, 900 °C, and 1,100 °C. Few studies have reported the effects of burning temperature on both the chemistry and toxicity of coal combustion particles. The highest mass emission factor of particulate matter less than 2.5 µm (PM_2.5) was found to be produced at 700 °C (3.51 g/kg), owing to strong elemental carbon (EC) emission and ash formation (ions and elements) resulting from the incomplete combustion of tar and char, and mineral fragmentation. The highest organic carbon in PM_2.5 was found at 550 °C. At a temperature higher than 700 °C, the fraction of carbonaceous species decreased while the fractions of ions and elements increased owing to ash formation. Sulfate was found to be the dominant ionic species, followed by sodium, calcium, and magnesium. The highest emission of elements (Al, As, Ba, Cd, Co, Cu, Fe, Mn, Ni, Pb, Sr, Ti, V, and Zn) and the highest fractions of Fe and Al were observed at 700 °C. Intrinsic OP activities obtained from dithiothreitol (DTT) and electron spin resonance (ESR) assays showed the highest values at 550 °C, suggesting that fine particles from low-temperature coal combustion had the highest reactive oxygen species generation capability (potentially toxic) among various tested burning temperatures. The results of principal component analysis suggested a correlation between OP-DTT activity and OC, EC, Cd, Co, V, and Zn, while OP-ESR activity was associated with chloride, nitrate, Ba, Pb, Sr, and Ti.