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 lack of detailed scientific experimental data, these atmospheric emissions and their impacts are mostly 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 made at three power plant loads, i.e., 30 MW, 60 MW, and 100 MW (full load), and at each of these loads, flue gas particles were characterized by comprehensive instrument setup both 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 combustion boiler reduced the particle number emissions three orders of magnitudes and the BC emissions close to zero. After the filtration, the measured primary particle number emissions were at 30 MW, 60 MW, and 100 MW 1.7∙10³ MJ^-1, 5.2∙10³ MJ^-1, and 7.2∙10³ MJ^-1, respectively. By number, emitted particles existed mostly in 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 authors knowledge, we observed that the secondary aerosol formation potential of the flue gas is high; the total impact of flue gases to atmospheric particulate matter concentrations can be even 100–1000 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.