Climate warming induced wildfires are rapidly increasing at high latitudes, yet their climate impacts remain poorly understood. These deeply smoldering fires may release long-stored carbon and thus perturbate the global carbon cycle and further emit light-absorbing carbonaceous particles enhancing snow and ice melt after deposition. We newly investigate the carbon isotopic and light-absorbing characteristics of carbonaceous particles produced in laboratory combustion experiments on Arctic-boreal peats and compare these with biomass from boreal forest and savanna environments. We provide the first observational evidence that boreal and especially Arctic peat smoldering may release millennial-aged carbon into the atmosphere, which upsets radiocarbon-based source attribution, separating fossil-fuel-derived sources from modern biomass. Moreover, above- and below-ground material combust differently, and hence the fraction of modern carbon (F14C), i.e., the average age, of the original biomass and the produced carbonaceous particles may differ. Furthermore, we show that peat smoldering produces significant amounts of Brown Carbon, which absorbs light at a similar magnitude to Black Carbon in these samples. Our results indicate that the increasing number of Arctic-boreal peat fires may exacerbate Arctic warming more than previously estimated.

Residential wood combustion (RWC) contributes significantly to urban air pollution; however, the influence of atmospheric aging on adverse health effects of RWC emissions remains uncertain. We exposed C57BL/6J mice in parallel with different in vitro models of first-line of defense cells (macrophages: RAW264.7 and lung epithelial cells: A549) at the air-liquid interface to either fresh or aged RWC emissions generated from an oxidation flow reactor. Both in vivo and in vitro cellular and molecular outcomes show that photochemically aged emissions play a key role in triggering lung inflammation and the polarization of macrophages into an M2 phenotype, bridging the gap between epidemiology and toxicology on inflammatory lung responses. Furthermore, evidence of protumorigenic activity in lung epithelial cells is detected after exposure to both emissions, but more pronounced after exposure to aged RWC emissions. This study highlights the importance of considering atmospheric aging in the assessment of air-pollution-related health effects.

The use of log wood stoves is common in residential homes and are tested in a type test procedure following EN 16510-1:2022 at optimal combustion condition. Since this does not represent real-life operation, a novel test protocol was developed and validated using two different log wood stoves. The new test protocol includes the ignition phase (two batches) at natural draught, followed by three batches at nominal load, two batches at partial load and one final batch at overload. Typical emission parameters such as carbon monoxide (CO), nitrogen oxides (NOX), organic gaseous carbon (OGC) emissions were recorded as well as TPM emissions in the hot undiluted flue gas. This study shows that it is challenging to get similar emission results for the same stove in different laboratories even when using the same fuel and well-defined test protocol, differences in results are due to measurement uncertainty, differences in appliance operations and not following exactly the defined Real-LIFE test protocol. Coefficients of variation for TPM, CO, OGC and NOX were 17.8%, 20.1%, 30.6% and 8.7%, respectively for stoveA and 32.7%, 13.9%, 19.6% and 10.0%, respectively for stoveB based on two to three repetitions per lab. The novel test protocol showed that combustion appliances may behave differently in different combustion phases, and this emphasizes the importance of measuring different combustion conditions in official testing to ensure that the appliances work properly in the field and that the measured emissions cover the whole operating range.

Residential wood combustion (RWC) is a major source of atmospheric particulate matter (PM). Yet, the diversity of PM emission measurement methods used for RWC appliances often leads to inconsistent and non-comparable results. This study compares two PM measurement techniques: a dilution-based method combining a porous tube diluter (PTD) and an ejector diluter (ED), and the heated filter method defined in EN 16510-1:2022 standard. A novel hybrid method was also introduced, integrating the EN standard with a PTD to separately quantify solid and condensable PM fractions. For the method comparison, emissions from six RWC appliances were measured across different combustion phases. Results show that both appliance type and combustion phase significantly affect emission composition, particularly the organic matter (OM) content, which in turn influences method comparability. The dilution method generally yielded higher PM concentrations, except when OM content was low. Due to the strong dependence on emission composition, universal conversion factors between methods were not feasible. The findings underscore the need for harmonized PM measurement protocols that account for condensable organic particles. The proposed hybrid method offers a more comprehensive assessment and is potential for future regulatory use.

Residential wood combustion (RWC) is an increasingly dominant source of particulate matter (PM) pollution in Europe. Electrostatic precipitators (ESPs) are a promising technology for controlling particle mass emissions from RWC appliances, but their influence on particle number concentrations (PNC) is highly variable, as they may occasionally increase PNC. In this study, we evaluated the effect of an ESP on PM1, black carbon (BC), elemental carbon (EC), organic carbon (OC), and particle number size distributions in emissions from wood-fueled stoves commonly used in Finland, under conditions spanning a wide range of upstream emission loads. Experiments were conducted in a state-of-the-art small-scale combustion simulation and measurement facility. The emission reduction efficiencies of the ESP were 75.7% +/- 4.7% for PM1, 83.2% +/- 14.2% for EC, and 70.1% +/- 12.6% for OC. The operation of ESP not only reduced PM1 concentrations but also influenced particle composition and optical properties with its differential collection efficiencies for EC and OC. Moreover, it reduced PNC within the size range of 0.13-2.5 & micro;m, but nucleation-mode PNC occasionally increased, suggesting possible new particle formation. Additionally, the combustion conditions that showed negative efficiencies for PNC had higher upstream organic gaseous carbon concentrations and higher OC : EC ratios compared to those with positive efficiencies, suggesting that organics-rich flue gas may contribute to increased PNC when ESPs are used. These findings highlight the importance of controlling organic emissions to improve the overall emission reduction performance of ESPs.

Residential wood combustion (RWC) is a major source of air pollutant emissions affecting air quality, human health and climate. Although widely studied, large RWC datasets remain scarce due to resource-intensive measurements. We analysed 674 measurements from 28 masonry heaters tested according to EN 15250:2007, in which the fuel load is combusted in up to five batch charges. Mixed-effects models quantified the effects of appliance technology, fuel properties and operating practices on gaseous and particulate emissions. Carbon monoxide (CO) and organic gaseous carbon (OGC) concentrations were highest during the ignition batch. Poor ignition of the subsequent batch increased OGC nearly 6-fold, making it the most variable component. Nitrogen oxides (NOₓ) were relatively stable but decreased approximately 10 % with optimised primary air staging compared with full primary air. Total suspended particle (TSP) concentration increased when sampling covered a greater part of the second batch cycle, indicating higher concentrations during later stages. Fuel moisture increased CO and OGC but had no clear effect on NOₓ or TSP at high excess air (λ); at low λ, increasing moisture decreased TSP. CO and OGC showed strong intercorrelation with a breakpoint between two linear ranges, while TSP was associated with elevated CO and OGC only above this point. This dataset supports emission factor definition for RWC appliances under near-real-life conditions. The results reveal unavoidable trade-offs between emissions and demonstrate that measured TSP should cover full combustion cycle. Ignition quality emerged as a critical variability source, underlining the need for robust appliance design and use.

Traditional biomass cooking remains a major source of household air pollution and climate-relevant emissions in South Asia, yet comparable emission data for commonly used cookstove technologies remain limited. This study evaluated the performance and emissions of eight biomass cookstove configurations representing gasifier, rocket, chimney, and traditional stove designs. Laboratory-based Water Boiling Tests (WBT) were conducted in Finland under controlled conditions using a partial-flow dilution system for particle sampling. Emissions were characterized with real-time gas analysers and extensive aerosol measurements, including fine particle mass (PM2.5), particle number (PN), alveolar-region lung-deposited surface area (ALV-LDSA), organic (OC) and elemental carbon (EC), equivalent black carbon (eBC), and polycyclic aromatic hydrocarbons (PAHs). Emission factors were calculated using WBT, carbon mass balance (CMB), and Finnish emission measurement standard -based methods to assess methodological consistency. The WBT and CMB methods produced largely consistent emission factors, indicating that simple CO2- and CO-based approaches provide reliable estimates for the main carbonaceous emissions. Stove performance and emissions varied substantially between technologies. The forced-draft gasifier showed the best performance and lowest emissions, whereas the chimney stove exhibited poor performance and high gaseous and particulate emissions, despite being classified as an improved stove. Phase-resolved analysis showed that refuelling periods produced transient emission peaks, especially for fan-assisted stoves. Tests without a cooking pot resulted in 40−96% lower emissions, demonstrating that stove–pot interaction strongly affected combustion conditions and emission formation. These findings underscore the need for integrated evaluation across performance indicators and multiple emission metrics to identify low-emission cooking technologies.

Clean cooking intervention and sustained use of them are crucial in achieving several sustainable development goals (SDG) including SDG 3, 7 and 13. This study aims to examine the impact of subsidy and distribution modality and sustainability of improved cook stove program (ICS) through retrospective assessments. The ICS distributed was an upgrade over inefficient traditional stoves, with a thermal efficiency of approximately 27 %, nearly twice the 15 % efficiency for the traditional stove. The study employs a mixed-methods approach, combining qualitative and quantitative elements to comprehensively evaluate the government-financed improved cook stove program in two rural municipalities of Nepal. This study uncovers the nuances of the ICS in study areas and reveal significant discrepancies between the intended outcomes of interventions and the actual practices and preferences of end-users. The results show that, although stoves are provided free of cost, sustained use was not ensured. Surprisingly, approximately 35 % of the end-users had exchanged their stoves for onions, especially those with low income. However, 22 % of the participants mentioned that they use the stove occasionally, particularly during rainy season and festivals. The adoption of the improved cookstove is ultimately determined by preference of the cookstove user. The study findings emphasized the needs of end-users' requirement while selecting the clean cooking options for better intervention outcomes. Nepal as a case study, the research contributes to the global discourse on clean cooking interventions, offering insights applicable to other low- and middle-income countries facing similar challenges. The findings of this study should inform policy and practice in diverse contexts and should encourage relevant stakeholders and policy makers to reevaluate their policies and program related with clean cooking intervention in Nepal.

Residential wood combustion (RWC) remains a significant global source of particulate matter (PM) emissions with adverse impacts on regional air quality, climate, and human health. The lung-deposited surface area (LDSA) and equivalent black carbon (eBC) concentrations have emerged as important metrics to assess particulate pollution. In this study we estimated combustion phase-dependent emission factors of LDSA for alveolar, tracheobronchial, and head-airway regions of human lungs and explored the relationships between eBC and LDSA in fresh and photochemically aged RWC emissions. Photochemical aging was simulated in an oxidative flow reactor at OH center dot center dot exposures equivalent to 1.4 or 3.4 days in the atmosphere. Further, the efficiency of a smallscale electrostatic precipitator (ESP) for reducing LDSA and eBC from the wood stove was determined. For fresh emission eBC correlated extremely well with LDSA, but the correlation decreased after aging. Soot-dominated flaming phase showed the highest eBC dependency of LDSA whereas for ignition and char burning phases non-BC particles contributed strongly the LDSA. Deposition to the alveolar region contributed around 60 % of the total lung-deposition. The ESP was found as an effective method to mitigate particulate mass, LDSA, as well as eBC emissions from wood stoves, as they were reduced on average by 72%, 71%, and 69%, respectively. The reduction efficiencies, however, consistently dropped over the span of an experiment, especially for eBC. Further, the ESP was found to increase the sub-30 nm ultrafine particle number emissions, with implications for LDSA. The results of this study can be used for assessing the contribution of RWC to LDSA concentrations in ambient air.

Residential biomass combustion significantly contributes to light-absorbing carbonaceous aerosols in the atmosphere, impacting the earth's radiative balance at regional and global levels. This study investigates the contribution of brown carbon (BrC) to the total particulate light absorption in the wavelength range of 370–950 nm (BrC370–950) and the particulate absorption Ångström exponents (AAE470/950) in 15 different European residential combustion appliances using a variety of wood-based fuels. BrC370–950 was estimated to be from 1 % to 21 % for wood log stoves and 10 % for a fully automatized residential pellet boiler. Correlations between the ratio of organic to elemental carbon (OC / EC) and BrC370–950 indicated that a one-unit increase in OC / EC corresponded to approximately a 14 % increase in BrC370–950. Additionally, BrC370–950 was clearly influenced by the fuel moisture content and the combustion efficiency, while the effect of the combustion appliance type was less prominent. AAE470/950 of wood log combustion aerosols ranged from 1.06 to 1.61. By examining the correlation between AAE470/950 and OC / EC, an AAE470/950 close to unity was found for pure black carbon (BC) particles originating from residential wood combustion. This supports the common assumption used to differentiate light absorption caused by BC and BrC. Moreover, diesel aerosols exhibited an AAE470/950 of 1.02, with BrC contributing only 0.66 % to the total absorption, aligning with the assumption employed in source apportionment. These findings provide important data to assess the BrC from residential wood combustion with different emission characteristics and confirm that BrC can be a major contributor to particulate UV and near-UV light absorption for northern European wood stove emissions with relatively high OC / EC ratios.

Residential combustion of brown coal can be an important source of ambient air pollution in areas with abundant brown coal deposits, such as Eastern Europe or China. The exhaust emission contents may vary regionally depending on the fuel composition, calling for detailed characterization of emissions from different coal types. In this work, the organic gaseous emissions of European brown coal combusted in a modern chimney stove -type residential appliance were measured by a proton transfer reaction time-of-flight mass spectrometer. Of three consecutive batches of brown coal briquettes, the first batch produced two-fold emission (144 ± 52 mg/MJ) of organic gaseous compounds (OGCs) compared to the later batches (71 ± 35 mg/MJ). The compositions between the batches were, however, relatively similar. Carbonyls accounted for 36 ± 3.0% of the identified emission factors, while aromatic hydrocarbons and oxygenated aromatic compounds contributed 19 ± 3.4% and 16 ± 1.8%, respectively. The complex and overlapping chemical processes within batch combustion were exposed by non-negative matrix factorization, giving insight into the temporal variation in the formation pathways of the OGCs. The OGCs were separated into five factors revealing the chemical fingerprints of the main processes leading to formation of, for example, substituted or single-ring aromatic hydrocarbons. Oxygenated aromatic compounds were related to a distinct factor, which was proposed to form specifically from decomposition of the lignin residues of the brown coal. OGCs from brown coal combustion were estimated to have notable secondary particle formation potential: in photochemical conditions, they may double the organic particulate emission, while reactions in dark conditions may lead to excessive nitrophenol formation.

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 (PM2.5) was mainly composed of elemental carbon (50–70% of PM2.5), 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.

Residential heating with solid fuels is one of the major drivers for poor air quality in Central and Eastern Europe, and coal is still one of the major fuels in countries, such as Poland, the Czech Republic, and Hungary. In this work, emissions from a single-room heater fueled with brown coal briquettes (BCBs) and spruce logs (SLs) were analyzed for signatures of inorganic as well as semivolatile aromatic and low-volatile organic constituents. High variations in organic carbon (OC) emissions of BCB emissions, ranging from 5 to 22 mg MJ-1, were associated to variations in carbon monoxide (CO) emissions, ranging from 900 to 1900 mg MJ-1. Residential BCB combustion turned out to be an equally important source of levoglucosan, an established biomass burning marker, as spruce logwood combustion, but showed distinct higher ratios to manosan and galactosan. Signatures of polycyclic aromatic hydrocarbons emitted by BCB combustion exhibited defunctionalization and desubstitution with increasing combustion quality. Lastly, the concept of island and archipelago structural motifs adapted from petroleomics is used to describe the fraction low-volatile organic compounds in particulate emissions, where a transition from archipelago to island motifs in relation with decreasing CO emissions was observed in BCB emissions, while emissions from SL combustion exhibited the island motif.

Effective density (ρeff) is an important property describing particle transportation in the atmosphere and in the human respiratory tract. In this study, the particle size dependency of ρeff was determined for fresh and photochemically aged particles from residential combustion of wood logs and brown coal, as well as from an aerosol standard (CAST) burner. ρeff increased considerably due to photochemical aging, especially for soot agglomerates larger than 100 nm in mobility diameter. The increase depends on the presence of condensable vapors and agglomerate size and can be explained by collapsing of chain-like agglomerates and filling of their voids and formation of secondary coating. The measured and modeled particle optical properties suggest that while light absorption, scattering, and the single-scattering albedo of soot particle increase during photochemical processing, their radiative forcing remains positive until the amount of nonabsorbing coating exceeds approximately 90% of the particle mass.

The combustion of wood in small-scale appliances emits significant amounts of particulate and gaseous pollutants into the atmosphere, leading to impaired air quality and adverse health and climate effects. Simple and easily implemented reduction techniques are needed to address this issue. In this study, different air staging strategies in a sauna stove were investigated with high temporal resolution, and the relationships between combustion air settings, combustion parameters, and different emission components were examined. Air staging was found to decrease PM1 and BC emissions by 43 and 41 %, and CO and OGC emissions by 23 and 42 %, respectively, when the stove was used in its standard configuration. Reducing and redistributing primary air decreased emissions further. BC emissions were lowest when the sauna stove was operated with an air-to-fuel ratio of 1.5. BC correlated weakly with gaseous emissions, with the exception of acetylene, highlighting the role of C2H2 as a precursor gas in soot formation. High OC/EC ratios during experiments with inefficient combustion conditions led to high average AAE values, which ranged from 1.23 to 1.41. Instantaneous AAE values correlated with concentrations of carbonyl compounds, especially acetaldehyde, suggesting that carbonyls may be indicative of BrC in wood smoke. The results show that significant emission reductions can be achieved in a simple combustion device with small, easily implemented modifications. In addition, the highly time-resolved data revealed relationships between various emission components, combustion conditions and the formation and properties of soot.

Solid fuel usage in residential heating and cooking is one of the largest sources of ambient and indoor air particulate matter, which causes adverse effects on the health of millions of peoples worldwide. Emissions from solid fuel combustion, such as biomass or coal, are detrimental to health, but toxicological responses are largely unknown. In the present study, we compared the toxicological responses regarding cytotoxicity, inflammation and genotoxicity of spruce (SPR) and brown coal briquette (BCB) combustion aerosols on human alveolar epithelial cells (A549) as well as a coculture of A549 and differentiated human monocytic cells (THP-1) into macrophages exposed at the air-liquid interface (ALI). We included both the high emissions from the first hour and moderate emissions from the third hour of the batch combustion experiment in one ALI system, whereas, in the second ALI system, we exposed the cells during the whole 4-hour combustion experiment, including all combustion phases. Physico-chemical properties of the combustion aerosol were analysed both online and offline. Both SPR and BCB combustion aerosols caused mild cytotoxic but notable genotoxic effects in co-cultured A549 cells after one-hour exposure. Inflammatory response analysis revealed BCB combustion aerosols to cause a mild increase in CXCL1 and CXCL8 levels, but in the case of SPR combustion aerosol, a decrease compared to control was observed.

The absorption Ångström exponent (AAE) describes the spectral dependence of light absorption by aerosols. AAE is typically used to differentiate between different aerosol types for example., black carbon, brown carbon, and dust particles. In this study, the variation of AAE was investigated mainly in fresh aerosol emissions from different fuel and combustion types, including emissions from ships, buses, coal‐fired power plants, and residential wood burning. The results were assembled to provide a compendium of AAE values from different emission sources. A dual‐spot aethalometer (AE33) was used in all measurements to obtain the light absorption coefficients at seven wavelengths (370–950 nm). AAE470/950 varied greatly between the different emission sources, ranging from −0.2 ± 0.7 to 3.0 ± 0.8. The correlation between the AAE470/950 and AAE370‐950 results was good (R2 = 0.95) and the mean bias error between these was 0.02. In the ship engine exhaust emissions, the highest AAE470/950 values (up to 2.0 ± 0.1) were observed when high sulfur content heavy fuel oil was used, whereas low sulfur content fuels had the lowest AAE470/950 (0.9–1.1). In the diesel bus exhaust emissions, AAE470/950 increased in the order of acceleration (0.8 ± 0.1), deceleration (1.1 ± 0.1), and steady driving (1.2 ± 0.1). In the coal‐fired power plant emissions, the variation of AAE470/950 was substantial (from −0.1 ± 2.1 to 0.9 ± 1.6) due to the differences in the fuels and flue gas cleaning conditions. Fresh wood‐burning derived aerosols had AAE470/950 from 1.1 ± 0.1 (modern masonry heater) to 1.4 ± 0.1 (pellet boiler), lower than typically associated with wood burning, while the burn cycle phase affected AAE variation.

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.

Air pollution emitted by residential biomass combustion (RBC) is a known cause of adverse health and climate effects. Currently, manufacturers of stoves and fireplaces are facing challenges due to tightening emission regulations, such as the Ecodesign Directive in the European Union. Consequently, there is a demand for new emission control solutions for RBC. Herein, a novel method has been introduced to reduce particulate emissions, namely: high-temperature electric soot collector (HiTESC). In this method, an electrically insulated high-voltage electrode is installed in a combustion chamber, which generates an electric field. Particles that acquire the electrical charges produced by flames are collected on the electrode surface and oxidized at high temperatures. A fine particle (PM1) reduction efficiency of 45% was achieved using this method in a logwood-fired masonry heater. The reduction efficiency of the method was found to be dependent on the combustion phase. The PM1 reduction was most efficient during the flaming conditions, when the PM emissions were the highest with the studied logwood appliance. The advantages of this method are its simple construction, low space requirement, and low energy consumption; further, it does not require a separate cleaning mechanism. The proposed method can be used in logwood-fired combustion appliances to achieve future emission regulation limits, without using costly exhaust after-treatment systems.