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Small-scale biomass combustion is an important source of fine particles in ambient air, causing adverse health and environmental effects. Thus, there is a clear need to develop efficient and feasible flue gas cleaning technologies for small-scale combustion appliances. In this study a novel electrical charging condensing heat exchanger (eCHX) for combined fine particle removal and efficient heat recovery from flue gases was demonstrated in a small biomass-fired boiler. The method is based on the combination of a shielded corona charger and a condensing heat exchanger, where fine particles are removed by the electrophoretic, thermophoretic and diffusiophoretic forces. The eCHX was found to decrease >80% of fine particle mass (PM1) emissions and >40% of particle number emissions with simultaneous high thermal efficiency in the heat exchanger. The usage of the condensing heat exchanger without electrical charging resulted in 40% decrease in PM1 emissions when compared to the usage of a traditional tube heat exchanger. The advantage of the eCHX system is that it replaces the conventional heat exchanger in boilers, making it a compact and inexpensive solution, when compared to additional flue gas cleaning devices installed after the boiler.

Interactions between anthropogenic and biogenic emissions, and implications for aerosol production, have raised particular scientific interest. Despite active research in this area, real anthropogenic emission sources have not been exploited for anthropogenic-biogenic interaction studies until now. This work examines these interactions using α-pinene and pellet boiler emissions as a model test system. The impact of pellet boiler emissions on secondary organic aerosol (SOA) formation from α-pinene photo-oxidation was studied under atmospherically relevant conditions in an environmental chamber. The aim of this study was to identify which of the major pellet exhaust components (including high nitrogen oxide (NOx), primary particles, or a combination of the two) affected SOA formation from α-pinene. Results demonstrated that high NOx concentrations emitted by the pellet boiler reduced SOA yields from α-pinene, whereas the chemical properties of the primary particles emitted by the pellet boiler had no effect on observed SOA yields. The maximum SOA yield of α-pinene in the presence of pellet boiler exhaust (under high-NOx conditions) was 18.7% and in the absence of pellet boiler exhaust (under low-NOx conditions) was 34.1%. The reduced SOA yield under high-NOx conditions was caused by changes in gas-phase chemistry that led to the formation of organonitrate compounds.

A study about the temporal variation of organic emissions from a modern wood log fired masonry heater was carried out with different gas analysis techniques: single-photon ionisation time-of-flight mass spectrometry (SPI-TOFMS) for real-time analysis of volatile (VOC), intermediate-volatile (IVOC) and semi-volatile organic compounds (SVOC), and a gas analyser system for gaseous components CO2, CO, NOx and organic gaseous carbon (OGC, quantified by flame ionisation detector). The emissions of three in Europe common types of firewood (beech, birch and spruce) were investigated by combustion of six consecutive batches of 2.5 kg each over 4 h. Batchwise emissions and temporal variations during combustion were discussed. Emission factors over the whole combustion cycle for OGC, VOC and IVOC were right up to one order of magnitude lower than in many previous studies due to latest improvements of air staging technology in wood log fired masonry heaters, whereas CO and NOx remained comparable. Regarding each combustion experiment, more than 50% of the total intensity of the mass spectra occurred during the combustion of the first two batches. Moreover, the molecular signatures of burning phases ('ignition', 'stable combustion' and 'ember') were examined by using non-negative matrix factorisation (NMF) and principal component analysis (PCA) in sequence. Marker substances for wood or biomass combustion, such as phenolic species or furan derivatives, exhibited highest relative abundance during 'stable combustion', whereas 'ember' is distinctly characterised by polyunsaturated hydrocarbons, such as benzene or naphthalene, through pyrosynthesis; in 'ignition', secondary decomposition products dominated. Nevertheless, highest quantitative emissions always occurred during 'ignition' at the beginning of each batch, followed by the phases 'ember' and 'stable combustion'.

Residential wood combustion (RWC) emits high amounts of volatile organic compounds (VOCs) into ambient air, leading to formation of secondary organic aerosol (SOA), and various health and climate effects. In this study, the emission factors of VOCs from a logwood-fired modern masonry heater were measured using a Proton-Transfer Reactor Time-of-Flight Mass Spectrometer. Next, the VOCs were aged in a 29 m(3) Teflon chamber equipped with UV black lights, where dark and photochemical atmospheric conditions were simulated. The main constituents of the VOC emissions were carbonyls and aromatic compounds, which accounted for 50%-52% and 30%-46% of the detected VOC emission, respectively. Emissions were highly susceptible to different combustion conditions, which caused a 2.4-fold variation in emission factors. The overall VOC concentrations declined considerably during both dark and photochemical aging, with simultaneous increase in particulate organic aerosol mass. Especially furanoic and phenolic compounds decreased, and they are suggested to be the major precursors of RWC-originated SOA in all aging conditions. On the other hand, dark aging produced relatively high amounts of nitrogen-containing organic compounds in both gas and particulate phase, while photochemical aging increased especially the concentrations of certain gaseous carbonyls, particularly acid anhydrides.

Gas-phase emission samples of carbonyl compounds (CCs) were collected from two modern wood combustion appliances. Multiple repetitions were conducted on masonry heater operated with three logwood species (birch, beech, and spruce) and for a pellet boiler operated by softwood pellet with normal combustion and unoptimized combustion (in which the secondary combustion air flow rate was decreased). The sampling of CCs was performed from diluted exhaust using 2,4-dinitrophenylhydrazine (DNPH) cartridges. The CCs-hydrazone derivatives were analyzed by a gas chromatography–selective ion monitoring–mass spectrometry (GC-SIM-MS) method. Twelve (12) CCs were quantified in the masonry heater emissions and 8 in the pellet boiler emissions. The total carbonyl emission factors (EFs) for logwood were determined to be as follows: birch, 113 ± 18 mg kg–1; beech, 178 ± 31 mg kg–1; spruce, 171 ± 19 mg kg–1; and, for softwood pellet with normal combustion, 6 ± 0.9 mg kg–1 and for softwood pellet with unoptimized combustion, ...

The emissions and ash behaviour during combustion of wood chips, or co-combustion of two solid agricultural fuels (reed canary grass and barley straw) with wood chips, were studied. In addition, the sensitivity of the results towards different air-staging conditions was investigated using pure wood chips. The experiments were carried out in a 40-kW combustion reactor equipped with a reciprocating-grate burner. The addition of the reed canary grass to the wood chips increased only slightly the emission of fine particles (PM1), nitrogen oxides (NOX) and sulphur dioxide (SO2); while carbon monoxide (CO), hydrogen chloride (HCl), organic carbon (OC), elemental carbon (EC) and the geometric diameter (GMD) of the particles either decreased or remained unchanged. However, the number of particles emitted increased 2-fold in the reed canary grass combustion compared to the pure wood chips. In contrast, the addition of straw to wood chips substantially increased the emissions of PM1, CO, EC, SO2 and HCl. The straw-originating particles were mostly crystalline KCl, and their number emission was clearly reduced, but their size was larger compared to the case with pure wood chips. The distribution of the combustion air had only a very minor influence on the release of the major ash species, whereas the effect was significant for the release of specific trace metals and the products of incomplete combustion. Finally, the partitioning of ash-forming elements with various fuels was evaluated based on chemical analyses of the fuel, bottom ash and fine fly ash fractions.

Small-scale pellet boilers and stoves became popular as a wood combustion appliance for domestic heating in Europe, North America and Asia due to economic and environmental aspects. Therefore, an increasing contribution of pellet boilers to air pollution is expected despite their general high combustion efficiency. As emissions of primary organic aerosol (POA) and permanent gases of pellet boilers are well investigated, the scope of this study was to investigate the volatile organic emissions and the formation potential of secondary aerosols for this type of appliance. Fresh and aged emissions were analysed by a soot-particle aerosol time-of-flight mass spectrometry (SP-AMS) and the molecular composition of the volatile precursors with single-photon ionisation time-of-flight mass spectrometry (SPI-TOFMS) at different pellet boiler operation conditions. Organic emissions in the gas phase were dominated by unsaturated hydrocarbons while wood-specific VOCs, e.g. phenolic species or substituted furans, were only detected during the starting phase. Furthermore, organic emissions in the gas phase were found to correlate with fuel grade and combustion technology in terms of secondary air supply. Secondary organic aerosols of optimised pellet boiler conditions (OPT, state-of-the-art combustion appliance) and reduced secondary air supply (RSA, used as a proxy for pellet boilers of older type) were studied by simulating atmospheric ageing in a Potential Aerosol Mass (PAM) flow reactor. Different increases in OA mass (55% for OPT, 102% for RSA), associated with higher average carbon oxidation state and O:C, could be observed in a PAM chamber experiment. Finally, it was found that derived SOA yields and emission factors were distinctly lower than reported for log wood stoves., final draft, peerReviewed