Work

Characterisation of gaseous and particulate emissions from small-scale biomass boilers (<400kW) under real operating conditions

Year: 2026

Type: article

Abstract: Small scale biomass boilers (SSBB, 50 to 400 kW) are increasingly deployed as renewable heating systems, promoted for their high energy and environmental performance under standardized laboratory conditions. However, their actual efficiency and atmospheric pollutant emissions under real operating conditions remain poorly documented. The aim of this study was to characterize particulate emissions from three SSBBs (two pellet-fired, one wood-chip-fired) over an entire heating season, focusing on mass, chemical composition and their oxidative potential (OP). Periodic on-site campaigns were conducted to measure emerging pollutants and metrics of interest, such as black carbon, PAHs, metals, inorganic salts, and OP. Their emission factors were determined and compared with existing literature. Results show that emitted particles consisted of a solid fraction and a condensable fraction, primarily made up of semi-volatile organic compounds. The condensable fraction represents approximately 10 % of the total particles for the pellet boilers and 17 % for the chip boiler. Solid fraction depends on the potassium and sodium content in the fuel, while the condensable fraction varies with the CO concentrations, reflecting incomplete combustion. Carbonaceous matter, accounting for less than 30 % of the total particles and metals for less than 3 %. Levoglucosan emissions were negligible, except during on/off operating modes, supporting the hypothesis that levoglucosan is better suited as a marker of low-efficiency wood combustion than an unequivocal tracer of biomass burning. In real operating conditions, PM concentrations occasionally exceeded NF EN 303-5 limits, primarily due to low-quality fuels (rich in K and Na) and suboptimal combustion settings. Preliminary OP levels of SSBB particles were lower than those reported for logwood stoves under the investigated conditions. However, these correlative associations, obtained on a limited sample of appliances, should be considered as preliminary and hypothesis-generating; a lower oxidative potential cannot be directly equated with demonstrated lower biological toxicity. These findings highlight the importance of fuel quality, optimized combustion control, and appropriate operation for ensuring both energy efficiency and reduced environmental impact of SSBBs in real-life use.

Source: Atmospheric Environment X

DOI: 10.1016/j.aeaoa.2026.100529