Indoor PM10 from fireplace, wood- and coal stove: morphology, composition, and oxidative potential in real residential settings

Residential combustion of solid fuels is a dominant source of indoor particulate matter (PM), with significant implications for human health. This study investigates the physicochemical properties and oxidative potential (OP) of indoor PM₁₀ generated during the operation of different combustion appliances (woodstove, fireplace and coal stove) and fuels in real residential settings. Indoor and concurrent outdoor samples were analysed for water-soluble organic carbon (WSOC), elemental composition, particle morphology, and OP using both dithiothreitol (DTT) and ascorbic acid (AA) assays. Biomass combustion, especially in the fireplace, resulted in the highest indoor PM₁₀, OC, and WSOC levels, with WSOC/OC ratios reaching up to 0.84, suggesting a large contribution from oxygenated organics. Morphological analysis by SEM-EDS revealed a mixture of carbonaceous soot, mineral ash, and spherical fly ash particles, with clear fuel dependence. Elemental analysis showed higher Ca, Cl, K, S and Mn concentrations during woodstove combustion, while indoor samples from coal burning displayed lower levels for most elements. The OP_V of indoor samples was consistently higher during wood combustion compared with coal or background air, showing significant correlations with OC, WSOC, and potassium.