Emissions characteristics of polycyclic aromatic hydrocarbons, water-soluble heavy metals, and oxidative potential from indoor non-energy combustion sources.

Indoor non-energy combustion, whose primary purpose is not to generate energy, is a major source of indoor particulate matter. This study analyzed polycyclic aromatic hydrocarbons (PAHs), water-soluble heavy metals (HMs), and dithiothreitol-based oxidative potential (OP) in total particulate matter (TPM) from incense coils, mosquito coils, moxa, joss paper, joss sticks, candles, and cigarettes. HMs derived from combustibles, while PAHs originated from incomplete combustion. Specially, 5-ring PAHs dominated in candle samples, whereas 3 - 4-ring were prevalent in other samples. Zn, Fe, Ba, and Cr were the primary water-soluble HMs, with Tl being an exception in mosquito coil samples, accounting for 50% of the total HMs. The mass-normalized oxidative potential (OP) of the indoor sources (0.87 - 8.84 pmol/min/μg) was lower than that of biomass burning, vehicle exhaust, and ambient PM, although OP rankings differed from those of PAHs and HMs. Water-soluble organic matter contributed 10.1-95.5% to OP across different sources. The yield ratio of TPM from cigarette sidestream smoke (SS) to mainstream smoke (MS) was 0.50, contrasting with those of HMs (0.71), PAHs (5.46), and OP (0.31). A negative correlation was observed between OP yields in MS and SS, while PAHs yield showed a positive correlation; no correlation was detected for TPM or HMs yield. These results indicate that employing different evaluation metrics to assess the health hazards of particles emitted from the combustion of indoor non-energy combustibles may yield divergent outcomes.