The increasing reliance on biomass for residential heating presents environmental benefits and challenges. Its combustion emits significant amounts of particulate matter (PM) and gaseous pollutants (CO2, CO, NOx, and organic gaseous emissions). Life Cycle Assessment (LCA) is widely used to evaluate the environmental impacts of anthropogenic activities. Existing databases are useful in the macroscopic perspective of residential heating; however, the diversity of small-scale biomass combustion in various decentralized applications may affect life cycle impact assessment. This pioneer study investigates the influence of biomass types by measuring particle and gaseous emissions from a residential wood boiler. Pollutant-specific emission factors (EFs) of four biomass fuels, including wood chips and pellets made of hardwood and softwood, were determined and integrated into the LCA. The results reveal up to two-fold differences in key impact categories (particulate matter, ozone formation, and terrestrial acidification potential). This study points out the need to integrate region-specific data derived from real measurements within LCA frameworks to improve the applicability and support decision-making in sustainable residential heating.

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.

Air-Liquid Interface (ALI) cell exposure systems are essential tools for assessing the toxicity of airborne aerosols and engineered nanomaterials in vitro. These systems are increasingly favored for depositing aerosols directly onto cell cultures with improved precision, scalability, and flexibility. However, a significant challenge remains in accurately determining the actual particle deposition, particularly for ultrafine particles (UFP, Dp <= 100 nm). This study investigates the chemical-based quantification of UFP mass deposition and the deposition variability across insert positions in an Automated Exposure Station (AES). Multi-well positions in the AES were exposed to soot UFP, rich in polycyclic aromatic hydrocarbons (PAH), and copper UFP for 4 h in independent experiments. To determine the mass deposition of soot UFP, Teflon-coated glass fiber filters were placed at various positions and analyzed to quantify targeted PAH. Similarly, copper UFP was deposited onto empty inserts in different positions, and post-exposure quantification was performed. Mass deposition efficiencies exhibited a high relative variability of 15 % from experiment to experiment, and the position-dependent variability was not significant for either soot UFP or copper UFP. However, compared to the results from a theoretical model, the model significantly underestimated mass deposition by a factor of 5-8. Incorporating an alternative calculation of the boundary layer thickness into the model improved the agreement between model and experimental data. Therefore, for UFP mass deposition results from modeling must be interpreted with care.

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.

Secondary organic aerosol (SOA) formed from wildfire/biomass-burning emissions (BB) represents a significant fraction of global SOA production. However, there are large uncertainties in representing BB-SOA in climate models. We studied the evolution of organic aerosols (OA) from burning three biomass samples─savannah grass, savannah wood, and boreal forest surface─under different combustion conditions and during daytime (photochemical oxidation) and nighttime (dark oxidation) aging in an atmospheric chamber. OA dominated the BB emissions by contributing ∼82-99% of the total PM1 mass. Atmospheric aging by both oxidation processes produced comparable amounts of net OA mass. We show, with PMF analysis, that this is connected to the more efficient loss of primary OA, which compensates for the more efficient gas-phase oxidation during daytime aging compared with nighttime. The observed moderate OA mass enhancement (0.75-1.3 times) agrees well with field observations, thereby addressing the discrepancy between laboratory and field studies. For both aging scenarios, total OA emission factors after aging are similar to those of primary OA, providing new insights into the evolution of BB emissions. Our results suggest a simplified treatment of OA in climate models in remote areas with low NOx concentrations.

Abstract Heavy-duty vehicles (including non-road mobile machinery, eg excavators), aircrafts and ships are contributing significantly to emissions of green-house gases and health-relevant air pollutants, such as fine airborne particulate matter (PM2.5) as well as emerging pollutants. For decarbonization of the sector, several new fuels, ranging from hydrogen via ammonia to synthetic eFuels are considered. An important question is how these potential new fuels will influence emissions of air pollutants and climate relevant compounds. LowC will address if these new fuels for high-power engines have an impact on the emissions of air pollutants and climate-drivers, considering also upstream emissions and secondary pollutants formed under different atmospheric conditions (daytime photochemical aging or night-time atmospheric radical chemistry). LowC will apply a series of state-of-the-art technologies to generate and characterize the emissions and assess the effects in lung cell models. The toxicological testing will be applied in a tiered manner (screening and in-depth verification), in line with visions of Toxicity Testing in the 21st Century. Emission data, including regulated and emerging pollutants, will feed into integrated assessment and atmospheric transport models, currently used to underpin EU policy and the Zero Pollution Action Plan, to assess impacts on the EU environmental policy objectives. Finally, LowC will evaluate health and environmental impacts and provide guidance and recommendations to ensure that solutions to reduce CO2 emissions and prevent climate change are safe and sustainable. The work is supported by the European Union’s Horizon Europe research and innovation program under Grant Agreement No. 101192913.

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.

Abstract Current mass-based regulation of ambient air particulate matter (PM) does not encompass source dependent variation in PM toxicity, the high numbers of ultrafine particles, or the impact of volatile and semi-volatile organic compounds (VOC/SVOC) from combustion emissions which contributes significantly to primary particle growth through condensation and secondary organic particle formation by atmospheric ageing. Therefore, fresh and photochemically aged exhaust emissions from Euro 6d-compliant cars (gasoline, diesel, and compressed natural gas), ship engines (heavy fuel oil and marine gas oil), and a jet combustor rig (JP-8 fuel), as well as model particles, were studied to better understand the properties driving toxicity. Effects (cytotoxicity, genotoxicity, cytokines, transcriptomics) were assessed in a 3D lung tissue model at air liquid interphase, and in vitro models of secondary tissues. Exhaust emissions from different transport modes varied considerably both in physicochemical characteristics and toxicological effects. This was further altered by photochemical ageing. Chemical composition appears to be a main driver of toxicity, while particle metrics (PM mass, number concentrations, and surface area) was poorly correlated with observed effects. The majority of biological responses induced by exhaust emissions were likely due to organic chemicals in the gas phase or adsorbed to particles species. The implications of this will be discussed in context of regulatory needs as well as the challenges this poses for in vitro toxicity testing, especially for the understanding of effects beyond the lung.

Particle linear depolarization ratio is a widely used parameter in lidar research to distinguish different aerosol types and the thermodynamic phase of water. It is most frequently measured at ultraviolet and visible wavelengths (355 and 532 nm), yet multi-wavelength observations suggest that this parameter can vary substantially with wavelength. In this work, we assessed particle linear depolarization ratios at 1565 nm using Halo Photonics StreamLine Doppler lidars. We examined the depolarization ratio through three case studies featuring extremely fresh and aged smoke, and volcanic ash aerosol particles in the troposphere. Both fresh and aged smoke aerosol particles induced low values. Specifically, aerosol layers dominated by extremely fresh smoke showed a depolarization ratio of 0.017 ± 0.004, whereas aged long-range transported smoke particles exhibited marginally higher values. Volcanic aerosol layers induced high depolarization ratios with layer mean values of 0.45 ± 0.01. For the extremely fresh smoke case, we further estimated the smoke mass concentration using the lidar observations at 1565 nm and found good agreement with the in situ observations. These results demonstrate that Halo Doppler lidars operating at 1565 nm wavelength are capable of distinguishing several key aerosol types, enabling a comprehensive characterization of atmospheric conditions by simultaneously observing aerosol properties and wind dynamics.

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.

Biomass combustion emits significant amounts of airborne particles, which have been recognized for their environmental and health risks for decades. Oxidative potential (OP) is one of the health-relevant metrics introduced frequently to assess airborne particles in recent years. This study investigates the OP offresh particulate matter with an equivalent aerodynamic diameter of less than or equal to 1 & micro;m (PM1) emitted from a residential biomass boiler (15 kW). Four biomasses, including hardwood chips, softwood chips, hardwood pellets, and softwood pellets, were studied. The sampled PM1 was characterized for its physicochemical properties and analyzed with two OP assays, including ascorbic acid (AA) and dithiothreitol (DTT). The average intrinsic OPAAm ranged from 0.005 to 0.018 nmol min-1 & micro;g-1, and volume-normalized OPAAv was 304.0 to 583.5 nmol min-1 m-3. For DTT assay, the range was 0.0002 to 0.004 nmol min-1 & micro;g-1 for OPDTTm, and 20.9 to 68.7 nmol min-1 m-3 for OPDTTv. More importantly, biomass types with high combustion-emitted PM emissions did not necessarily exhibit high OP, highlighting particle chemical composition as a key determinant of OP. Significant correlations were observed between the organic carbon (OC) fraction and intrinsic OP, underscoring the role of particulate organic components in driving OP from biomass combustion emissions. These findings emphasize the importance of multi-assay OP approaches and provide critical insight into the contribution of combustion emissions from different biomass fuels to ambient air.

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.

Wildfire smoke strongly affects air quality, human health, climate, and the Earth system. During atmospheric aging, wildfire aerosol particles undergo complex chemical and microphysical transformations that modify their optical properties, radiative effects, and cloud-forming ability. Of particular interest are organic surface coatings, which can enhance light absorption through lensing effects and increase particle hygroscopicity.Here, we present single-particle mass spectrometry measurements from a boreal forest wildfire smoke experiment, resolving the coexistence of hydrophilic compounds and hydrophobic polycyclic aromatic hydrocarbons (brown carbon) within individual particles. We show that glyoxal and methylglyoxal are directly emitted during combustion, contributing to the initial hygroscopicity of freshly emitted particles. During photochemical aging, rapid oxalate formation is observed, accompanied by a moderate increase in hygroscopicity, while PAH signals decrease on a slower timescale. The decay rates of individual PAHs are similar but show a clear dependence on relative humidity, indicating that PAH degradation is controlled by viscosity-dependent radical diffusion into the particles. In contrast, highly oxidized products form on much shorter timescales, suggesting that these reactions are largely confined to the particle surface. At elevated relative humidity, surface oxidation continues, whereas it rapidly ceases under dry conditions. These observations highlight the central role of relative humidity in controlling the microphysical properties, optical effects, and cloud activation potential of aged wildfire smoke.

Particulate matter (PM) from marine traffic interacts with solar radiation and clouds, ultimately influencing Earth's radiative balance. Ships operated with conventional fossil fuel oils emit light-absorbing carbonaceous PM that offsets aerosol-driven cooling and can even exert a net positive radiative forcing, i.e. warming effect. Radiative properties of PM are possibly further altered by atmospheric aging processes, the effects of which are not fully understood. We present black carbon (BC) emission factors (EF) and optical properties of fresh and photochemically aged particle emissions from a marine engine, operated using low-sulfur heavy fuel oil (LS-HFO) and marine gas oil (MGO), complying with recent maritime sulfur regulations by the International Maritime Organization (IMO). The fresh particle emissions comprised mostly BC, with average BC EFs of 144 and 43.2 mg/kWh for LS-HFO and MGO, respectively. Light absorption was mostly attributed to BC in particles from both fuels, with absorption & Aring;ngstr & ouml;m exponent (AAE, 370 to 880 nm) values 0.9-1.0 (interquartile range), and 870 nm single scattering albedo (SSA) values 0.15-0.24 during the full cycles. Fresh LS-HFO emissions exhibited lower SSA values than those of high-sulfur fuels reported in literature, primarily associated with reduced sulfate emissions. Photochemical aging led to an absorption enhancement (Eabs) of 1.2-1.5 and an increase in SSA relative to fresh emissions, although SSA remained below 0.5, and the estimated direct radiative forcing effect stayed positive. Our results show that sulfur-compliant marine fuels can emit highly absorbing particles with an atmospheric warming potential, which is mostly maintained even after photochemical aging.

Abstract. Biomass burning (BB) emits large amounts of pollutants in the particle and gas phases, with significant implications for air quality, human health and climate. Here, we investigate the emission of organic vapors from controlled burns of relatively understudied biomass fuels: woody plants and grasses from African savannah and European boreal forest surface using a high-resolution proton transfer reaction-mass spectrometer. To understand the effect of different oxidation regimes, organic vapors were aged in a 29 m3 Teflon chamber, where photochemical and dark aging were simulated. The average total primary emission factors (EFs) for organic vapors varied considerably with fuel type, ranging from 69 to 161 g kg-1. Photochemical aging led to substantial depletion of furanics, phenolics and oxygenated aromatics, accompanied by enhancements of carbonyl B compounds and O-containing compounds C<6 across experiments. In contrast, dark aging under low-NOx conditions produced minimal compositional changes. Hierarchical clustering of relative composition showed clear regime dependence, with regime-associated differences accounting for 73 % of the variance in group-level composition. Toluene and furan showed a strong negative correlation with secondary oxygenated volatile organic compounds (OVOCs), including anhydrides and small acids, consistent with their role as precursors. After 0.5 equivalent day of photochemical aging, organic vapors shifted to higher O/C (>0.70) and an increased fraction of CxHyOz (z≥3). These results highlight the integral role of OH·-driven photo-oxidation in governing the atmospheric evolution and composition of BB organic vapors and underscore the need for secondary organic aerosols (SOA) models to include non-traditional precursors.