Sauna Stoves (SS) are simple wood combustion appliances used mainly in Nordic countries. They generate emissions that have an impact on air quality and climate. In this study, a new measurement concept for comparing the operation, thermal efficiency, and real-life fine particle and gaseous emissions of SS was utilized. In addition, a novel, simple, and universal emission calculation procedure for the determination of nominal emission factors was developed for which the equations are presented for the first time. Fine particle and gaseous concentrations from 10 different types of SS were investigated. It was found that each SS model was an individual in relation to stove performance: stove heating time, air-to-fuel ratio, thermal efficiency, and emissions. Nine-fold differences in fine particle mass (PM₁) concentrations, and about 90-fold differences in concentrations of polycyclic aromatic hydrocarbons (PAH) were found between the SS, when dry (11% moisture content) birch wood was used. By using moist (18%) wood, particle number and carbon monoxide concentrations increased, but interestingly, PM₁, PAH, and black carbon (BC) concentrations clearly decreased, when comparing to dry wood. E.g., PAH concentrations were 5.5–9.6 times higher with dry wood than with moist wood. Between wood species, 2–3-fold maximum differences in the emissions were found, whereas about 1.5-fold differences were observed between bark-containing and debarked wood logs. On average, the emissions measured in this study were considerably lower than in previous studies and emission inventories. This suggests that overall the designs of sauna stoves available on the market have improved during the 2010s. The findings of this study were used to update the calculation scheme behind the inventories, causing the estimates for total PM emissions from SS in Finland to decrease. However, wood-fired sauna stoves are still estimated to be the highest individual emission source of fine particles and black carbon in Finland.

Residential wood combustion (RWC) is a significant source of gaseous and particulate emissions causing adverse health and environmental effects. Several factors affect emissions, but the effects of the fuel wood species on emissions are currently not well understood. In this study, the Nordic wood species (named BirchA, BirchB, Spruce, SpruceDry, Pine and Alder) were combusted in a modern stove, and the emissions were studied. The lowest emissions were obtained from the combustion of BirchA and the highest from Spruce and Alder. The fine particle mass (PM_2.5) was mainly composed of elemental carbon (50–70% of PM_2.5), which is typical in modern appliances. The lowest PAH concentrations were measured from BirchA (total PAH 107 µg/m³) and Pine (250 µg/m³). In the ignition batch, the PAH concentration was about 4-fold (416 µg/m³). The PAHs did not correlate with other organic compounds, and thus, volatile organic compounds (VOCs) or organic carbon (OC) concentrations cannot be used as an indicator of PAH emissions. Two birch species from different origins with a similar chemical composition but different density produced partially different emission profiles. This study indicates that emission differences may be due more to the physical properties of the wood and the combustion conditions than to the wood species themselves.

New particulate matter (PM) filtering technologies are needed to meet the emission regulations for small combustion appliances. In this work, we investigate the performance of a novel electrical particle filtration system, the single needle shielded corona charger (SCC), which offers an advantageous solution for PM control in boilers by enhancing particulate deposition within existing boiler sections. Experiments under different operating conditions of a wood-fired boiler were performed, wherein the SCC was installed upstream of either a condensing heat exchanger (CHX) or a cyclone. PM reduction was found to be strongly affected by the SCC temperature and the following collection surface area, and reached its highest reduction efficiency of >90% at the temperature range of 400–500 °C when operating in combination with a CHX. The SCC–cyclone combination was less efficient, providing a 27% PM reduction, as a result of the low surface area and residence time in the cyclone. These results indicate that the SCC can feasibly provide particle filtration when combined with a CHX, wet scrubber, or a cyclone to meet the new emission regulation requirements. The system is best suited for small-scale boilers but can be scaled up to larger boilers by increasing the number of corona chargers.