Fine Particle Emissions from Sauna Stoves: Effects of Combustion Appliance and Fuel, and Implications for the Finnish Emission Inventory

Abstract

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.

Variation of Absorption Ångström Exponent in Aerosols From Different Emission Sources

“…However, once emitted these wood combustion derived aerosols go through atmospheric aging processes, and based on some literature studies (Kumar et al., 2018; Saleh et al., 2013; Tasoglou et al., 2017), aged emissions may have higher AAE values than fresh emissions (e.g., due to the coating of BC particles and secondary organic aerosol formation). Also, the wood combustion in stoves might not be as optimal in reality as in our laboratory experiments (e.g., not dry wood or sweep‐cared chimneys) which may produce wood burning‐derived aerosols with higher AAE values (Tissari et al., 2019). Furthermore, the variation in wood combustion appliance types is very large (e.g., old masonry heaters, masonry ovens, open fireplaces, wood stoves) and their impacts of AAE values have not been studied.…”

“…These estimates are presented for the high time resolution and for the used averaging times. The very high maximum uncertainty in the case of the sauna stove emissions was due to the reason that the tape advance threshold was disallowed during the burn cycle (Tissari et al., 2019), which caused the attenuation rise to high values (on average to ATN 470 ≈280).…”

“…Two different commercially available sauna stoves were selected for this study (stove 1 and stove 2 here correspond to S1_11 and S6_11 in Tissari et al. (2019), respectively), of which stove 1 was known to emit moderately low PM emissions, whereas the stove 2 was a high PM emitter stove. The combustion period lasted for approximately 90 min during which three batches of wood (total amount 7 kg) were combusted.…”

“…The effect of exhaust pretreatment before the measuring instruments was HELIN ET AL. -Saksa et al (2016-Saksa et al ( , 2018 Buses Diesel, hybrid and alternative fuels Controlled driving conditions at depot area Pirjola et al (2015), Saarikoski et al (2017) Buses Diesel In-traffic conditions Järvinen et al (2019) Coal-fired power plant Coal and coal mixed with wood pellets Stack gas measurements with and without cleaning Mylläri (2018), Mylläri et al (2017Mylläri et al ( , 2019 Wood burning Three logwood species and softwood pellets Modern masonry heater, pellet boiler Czech et al (2018), Kanashova et al (2018), Kortelainen et al (2018), Reda et al (2015) Wood burning Birch logwood Sauna stove Tissari et al (2019) (Aakko-Saksa et al, 2016;Amanatidis et al, 2018). In addition, a potential aerosol mass (PAM) chamber was used to simulate aerosol aging and secondary aerosol formation (Kang et al, 2007;Lambe et al, 2011).…”

Sources of black carbon at residential and traffic environments

“…Compared to the 480  values obtained from the biomass burning emission measurements, Martinsson et al (2015) have reported the  values between 0.9 and 1.3 for the burning of birch logs in a conventional wood stove, however,  increased to above 2 when fuel was added. For various sauna stoves,  has been measured to be 1.17-1.33, but when wood had high moisture content,  was larger (1.6;Tissari et al, 2019). In ambient measurements,  can be larger than that measured directly from the emission source as  values for biomass burning emissions have been shown to 485 increase due to the atmospheric oxidation processes simulated with a smog chamber (Tasoglou et al, 2017).…”