Integrated assessment of volatile organic compounds from industrial biomass boilers in China: emission characteristics, influencing factors, and ozone formation potential

Industrial biomass boilers (IBBs) are widely promoted in China as a type of clean energy. However, they emit large amount of volatile organic compounds (VOCs) and the emission characteristics and the underlying factors are largely unknown due to the sampling difficulties. In this study, three wood pellet-fueled and two wood residue-fueled IBBs were selected to investigate the characteristics of VOC emissions and to discover their underlying impacting factors. The emission factor of VOCs varied from 21.6 +/- 2.8 mg/kg to 286.2 +/- 10.8 mg/kg for the IBBs. Oxygenated VOCs (OVOCs) were the largest group, contributing to 30.3 - 73.6% of the VOC emissions. Significant differences were revealed in the VOC source profiles between wood pellet-fueled and wood residue-fueled IBBs. Operating load, excess air, furnace temperature, and fuel type were identified as the primary factors influencing VOC emissions. The excess air coefficient should be limited below 3.5, roughly corresponding to the operating load of 62% and furnace temperature of 630 degrees C, to effectively reduce VOC emissions. VOC emissions also showed great differences in different combustion phases, with the ignition phase having much greater VOC emissions than the stable combustion and the ember phases. The ozone formation potential (OFP) ranged from 4.3 to 31.2 mg/m(3) for the IBBs, and the wood residue-fueled IBBs yielded higher OFP than the wood pellet-fueled ones. This study underscored the importance of OVOCs in IBB emissions, and reducing OVOC emissions should be prioritized in formulating control measures to mitigate their impacts on the atmospheric environment and human health.