Characterization of gaseous and particulate atmospheric emissions, including the condensable particulate fraction, from small biomass boilers (150 kW-1.65 MW) in France

Biomass combustion is the primary source of renewable energy in France. However, it also significantly contributes to outdoor air pollution. This energy sector is undergoing major changes, including evolving regulations, improved fuel types, and enhanced emission control technologies. While the performance of larger installations (>1 MW) is well documented, less is known about biomass boilers with lower capacities. It has become crucial to better understand the operation of smaller biomass boilers, assess their contribution to atmospheric pollution, and identify methods to reduce their emissions. The ACIBIOQA project investigated emissions from six biomass boilers with nominal power outputs ranging from 150 kW to 1.65 MW across France. Measurements included combustion gas-phase characterization (O 2 , CO 2 , CO, NOx, and organic gaseous compounds: OGCs) and particulate-phase characterization, covering total particulate matter (TPM), including both solid (SP) and condensable fractions, PM 10 , PM 2.5 , and PM 1 by mass, 15 heavy metals, 8 polycyclic aromatic hydrocarbons (PAHs). Measured concentrations (corrected to 6 vol% O 2 ) varied widely: CO ranged from 153 to 8841 mg Nm −3 , NOx from 172 to 395 mg eq. NO 2 Nm −3 , and organic gaseous compounds from <1 to 634 mg eq. C Nm −3 . TPM ranged from <1.5 to 475 mg Nm −3 , with SP between <0.3 and 475 mg Nm −3 . The condensable fraction contributed 4–26 % to TPM. PM 1 dominated the mass size distribution, accounting for 60–100 %. PAHs ranged from 0.1 to 340 μg Nm −3 , and heavy metals from 0.03 to 6.7 mg Nm −3 . Emission levels were influenced by boiler nominal power output, combustion load, operating regime, and filtration technology. Particularly, CO, OGCs, and PAHs were highest under unstable and low-load conditions. SP emissions increased with the number of combustion cycles and decreased operating load, while bag filters appeared to reduce SP levels. Higher condensable fractions were observed in boilers with complete on/off cycles and lower nominal outputs. This study provides new insights into emissions from small biomass boilers and represents a pioneering effort to characterize the condensable particulate fraction at the national level. Emission factors were calculated and compared with literature and national inventory values. • Emissions from six small biomass boilers (150 kW–1.65 MW) were characterized across France. • Emission levels were influenced by boiler nominal power output, combustion load, operating regime, and filtration technology. • CO, OGC, and PAH emissions were highest under unstable and low-load combustion conditions. • Solid particle (SP) emissions increased with combustion cycling and decreased load, while bag filters effectively reduced SP levels. • Higher condensable particulate fractions occurred in boilers with on/off cycles and lower nominal outputs. • The study provides new insights into emissions from small biomass boilers and is a pioneering effort to characterize the condensable particulate fraction at the national level.