Dwindling Aromatic Compounds in Fine Aerosols from Chunk Coal to Briquette Combustion

As the implementation of clean coal policies in China, the chunk coal has been gradually replaced by briquette coal in domestic energies. In this study the molecular composition of fine particles (PM2.5) from chunk and briquette coal combustion is characterized using the Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). More than 6,000 molecular formulae were detected in each PM2.5 sample. A remarkable decrease in unsaturation and aromatic compounds was found from chunk coal to briquette derived aerosols. Around 73.6% of the unique CHON compounds in chunk coal are considered to have aromatic structures, while it decreased to 7.3% in briquette. Most of these nitroaromatics detected only in chunk coal are highly carcinogenic and mutagenic with 4-6 rings. Moreover, the aromatic compounds in sulfur-containing compounds also showed a significant decrease. Meanwhile, because of the perforated shape and the additives during the production of briquettes, there are more heteroatoms-containing molecules released from briquette combustion, which are highly functional compounds with high molecular weight, high degree of oxidation, and low volatility. Our results provide molecular level evidence that the transformation from chunk coal to briquette effectively reduces the aromatic compounds, which is beneficial to assessing and reducing the human health impacts