Primary particle emissions and atmospheric secondary aerosol formation potential from a large-scale wood-pellet-fired heating plant

Abstract. Solid biofuels are one option to reduce fossil fuel combustion and mitigate climate change. However, large-scale combustion of solid biofuels can have significant impacts on air quality and the emissions of short-lived climate forcers. Due to the lack of detailed scientific experimental data on aerosol emissions, these atmospheric emissions and their aerosol impacts are largely unknown. In this study, we characterized primary particle emissions before and after the flue gas cleaning, as well as the potential of emissions to form secondary particulate mass in the atmosphere from the compounds emitted from a large-scale, biomass-fired modern heating plant. Experiments were conducted at three power plant loads, i.e., 30, 60, and 100 MW (full load), and, at each of these loads, flue gas particles were characterized for their physical and chemical characteristics. The study highlights the importance of efficient flue gas cleaning in biofuel applications; the bag-house filters (BHFs) utilized to clean the flue gas from the combustion boiler reduced the particle number emissions by 3 orders of magnitude, and the black carbon (BC) emissions were close to zero. After the filtration, at 30, 60, and 100 MW, the measured primary particle number emissions were 1.7 × 103, 5.2 × 103, and 7.2 × 103 MJ−1, respectively. By number, emitted particles existed mostly in the sub-200 nm mobility particle size range. When measuring the potential of flue gas to form secondary aerosol in the atmosphere, for the first time, according to the authors' knowledge, we observed that the secondary aerosol formation potential of flue gas is high; the total impact of flue gases on atmospheric particulate matter concentrations can even be 100 to 1000 times higher than the impact of primary particle emissions. In general, the results of the study enable emission inventory updates, improved air quality assessments, and climate modeling to support the transition toward climate-neutral societies.