18.2 Houtrookvrij -Science Nanoparticle emissions from residential wood combustation 2019

Combustion conditions Particle size and composition Efficient Particle diameter < 100 nm, irregular shape. Most particles were ash with crystalline nuclei; some identi fied as zinc oxide. Intermediate Particles appeared to be more spherical in shape with coating of organic matter. Sizes ranged from 40 to 150 nm with the largest particles making agglomerates that contained ash, soot and organic matter. Smoldering Almost all large branched soot agglomerates. Some inorganic elements were detected, but were mostly a mixture of soot and POM with a minor amount of ash. R. Trojanowski, V. Fthenakis Renewable and Sustainable Energy Reviews 103 (2019) 515–528 523 found the start-up and flaming phase were characterized by small particle diameters whereas smoldering conditions had larger particle diameters. Number concentrations were greatest during the start-up phases and especially for cold start-up phases but were lower for smoldering phases. A group in France looked at the mass and number distributions of wood combustion particles emitted from beech cordwood (12% moisture content) during normal and reduced operation from two dif- ferent fireplaces; one a conventional fireplace (13 kW) with only pri- mary air intake from the front and the other was a more compact ‘next generation’ fireplace (4 kW) with primary and secondary air intake.

Measurements were taken from a dilution tunnel using a gravimetric based filter measurement and ELPI. Surprisingly, the study found the opposite trend of most, in that the older technology was more favorable to less particulates but ultimately showed agreement that more NPs were produced in the newer technology. The study found the next generation fireplace produced much higher particle emission numbers for than the conventional fireplace; speci fically, for the reduced con- ditions, the emission numbers were 50 times greater in the more modern fireplace than the older conventional unit [73]. While 80% and 60% (total number of particles) of the total PM consisted of particles with a diameter less than 100 nm, for the new and old fireplaces, re- spectively, it only contributed to a very small extent of the total mass of the aerosol; 5.5 –5.8% and 2.6 –0.3% for the new and old fireplaces, respectively during normal and reduced operations [73]. Another group in Finland looked at the PM and gaseous emissions from both normal and smoldering wood combustion periods in a con- ventional masonry heater made of soapstone using birch cordwood at 7% moisture content.

The results from the study showed a higher particle emission number measured in a dilution tunnel by the ELPI and FMPS during the normal combustion and less than half the particle emission number during smoldering state with geometric mean dia- meters of 56 and 65 nm by FMPS and ELPI measurements, respectively, for normal combustion, and 118 and 160 nm values for smoldering combustion [55]. Surprisingly for cordwood combustion, the repeat- ability was good. Even if all operating parameters are kept constant, manual fed cordwood appliances are very variable [58]. The study found the average particle number size distribution for normal com- bustion to be unimodal at 65 nm and the smolder combustion to pro- duce a bimodal distribution with peaks at 70 and 250 nm [55]. In ad- dition, SEM and TEM analysis from the hot stack showed both spherical and irregular shaped particles making up larger agglomerates and fine ash particles remained as separate particles. Normal combustion showed spherical and irregular shapes while smoldering combustion showed more irregular and sintered-like structures. The elemental analysis showed single particles were composed mainly of carbon, but also contained K, S, Zn, and less commonly O, Ca, Fe, Mg, Cl, P and Na were found [55].

Similar to studies mentioned above, particle material volatized under the beam indicating the presence of heavy organic compounds. The group was able to suggest the shifting of particle size during the di fferent combustion conditions seemed to be determined by the amount of condensed organic vapor in the flue gas [55]. Table 3 Summary of average particle size from cited sources. Equipment Summary: average particle sizes are given unless otherwise speci fied References Cordwood Stoves Start up: 180 –260 nm Steady state: 30; 107; 175 –180 nm Burn out: 30 –60 nm; 180 –200 nm Burn out or start up showing the highest concentrations of NPs and steady state having the lowest concentrations of NPs In some studies, aggregations of NPs with diameters of 313 –662 nms Low MW PAHs favored small NP diameters & High MW PAHs favored coarse particles Increase in oxygen in combustion chamber caused for smaller particles Decrease in oxygen caused PAH levels to increase and bind to NPs Image: high temperature combustion produced carbon aggregations with single particles having a single nuclei and turbostratic structure; low temperature combustion produced carbon dominated spherical particles [56,61–65,67] Pellet Stoves 7–30 nm Steady state showed lowest concentrations of NPs [67,68] Cordwood Boilers 60–180 nm; but as small as 12 nm to as large as 400 nm Highest concentrations seen during start up

Advanced boilers produced smaller particles and lower concentrations than traditional boilers PAHs higher in older boiler technology [31,58] Pellet Boilers 60–130 nm (no bark pellets) 220 nm (bark pellets) No obvious trend was observed between full and intermittent output in terms of particle size, only a very slight increase in mass concentration. Particles were likely inorganic salts [9,18,31,56,61,69] Chip Boilers Steady state: 25 –75 nm; lowest particle concentrations Modulating: 65 nm Smolder: 160 –200 nm; highest particle concentrations Lower excess air values led to lower particle counts and larger particles, however another group found greater concentrations with increased oxygen SEM & TEM images indicated di fferent types of particles; agglomerates of spherical compact particles, perfectly spherical representing coal fly ash or irregular shaped crystalline platelets.

E fficient was typically salts and crystalline while intermediate was a variety of soot agglomerates and ash; smolder was large agglomerates of soot PAHs bound to NPs lowest during e fficient burns and highest during smoldering conditions [21,56,63,70] Fireplaces and Masonry Heaters 10–20 nm; 50 –65 nm; 170 nm 70–250 nm during smoldering 100–326 nm range assumed to be agglomerates owed to cooling Start-up had highest concentrations; steady state had lowest Decrease in oxygen corresponded to decrease in NPs Newer technology stoves seemed to produce more NPs Agglomerates with individual particles spherical in shape Normal combustion showed spherical and irregular shapes while smoldering combustion showed more irregular and sintered-like structures Some salts but a presences of heavy organic compounds as well [2,55,71–73] R. Trojanowski, V. Fthenakis Renewable and Sustainable Energy Reviews 103 (2019) 515–528 524 In addition to the work done by Lamberg et al. [9] on a pellet boiler, the group also studied three conventional masonry heaters and one modern masonry heater made of soapstone. All masonry heaters burned birch logs with a low moisture content (10 –13% on a dry basis). The group explored continuous combustion, steady-state periods, cyclic operation, and ignition phases. Overall, GMD sizes ranged from 63 nm to 142 nm.

The largest diameters were found during incomplete com- bustion phases and also produced bimodal number and size distribu- tions; the ignition phase also produced a larger GMD [9]. Similar to the pellet boiler discussed above, the most abundant PAHs were pyrene and fluoranthene in addition to phenanthrene and cyclopenta[ c,d]pyrene for one of the masonry heaters. Total PAH emissions from PM 1 emis- sions (PAH/PM 1) were higher than that of the pellet boiler but still reasonably low with a range of 0.15 –2.8%. 7. Discussion This literature review revealed two earlier review papers and about eighty research articles and reports. An earlier review by Kumar et al. reports only limited information on NP emissions from non-vehicles exhaust sources [74]; the authors reported only two studies associated with NP emissions in RWC. The current review identi fied and reviewed many more studies that explicitly or implicitly provide information regarding NP emission data from RWC. However, measuring and quantifying the presence of NP in emissions, and how these emissions vary based on fuel, appliance type, and combustion period are not al- ways well investigated making correlations hard to draw. The second major review by Bølling et al.

(2009) pointed out there has been a lot of work done in steady-state operating conditions but there is limited data on particles from conventional cordwood boilers, modern wood stoves, and modern cordwood boilers [10]. The current review shows that this statement still holds true eight years later. Table 3 below summarizes the information collected from the papers above. In addition, cold starts, modulation periods, and in-e fficient burns exist and there may be an underestimation of real-life emissions which contain particle frac- tions that can be associated with health impacts in local areas [56].A s reported by Tom et al. [75], the majority of published studies were associated with laboratory experiments and field performance mea- surements were lacking. There is a signi ficant need to characterize the particle types in biomass smoke, since the regional and global climate e ffects of aerosols from biomass burning depend so strongly on particle properties [17]. However, manually fed cordwood stoves and boilers have a tendency to vary in their burn conditions even if fueled exactly the same way.

Schmatloch and Brenn directly observed this when fueling a cordwood furnace and trying to reproduce the size distribution in particles; burn one had much fewer concentrations of NPs less than 140 nm and greater amounts of NPs larger than 220 nm than burn two which showed op- posite trends [58]. This is owed to the nature of wood- how it burns and falls within the combustion chamber. This makes reproducibility very difficult and particle size distributions to have a larger variation than advanced automatic feed boilers [58]. This statement compliments the findings by Gaegauf et al. [56]. This also makes it di fficult to compare particle size distribution among studies. To complicate matters, Baer indicates that nanoparticles are inadequately characterized since they change with time and can be altered or damaged during analysis [76], so precautions must be taken to not bias research. Some key factors which may cause some uncertainty are sampling locations, sampling temperatures, and dilution ratios [74]. Ozgen et al. point out that the variability of the results concerning the number emissions and the size distribution during di fferent stages of the wood burning cycle suggests that emissions are strongly connected to the combustion conditions depending on the appliance design and operation [72]. The study by Johansson et al.

[31] emissions from pellet boilers were closer to those of an oil burner while old-type wood boilers had the highest. An important piece from the study was that emissions from the old-type wood boiler could be reduced if it was connected to a storage tank, similar to advanced modern units, higher quality fuel (lower moisture content) was used, or if fuel amount was decreased and small batches of fuel were loaded instead of a full charge. The study found poorer combustion conditions increased the amount of particles smaller than 100 nm. Finally, the group compared the wood combus- tion devices to oil burners finding pellet systems rivaled oil burners but old-type wood boilers would have low e fficiencies, high PM emissions, and unoxidized gaseous compounds [31]. While advanced systems that employ multiple control devices may decrease the amount of PM emission concentrations as well as reduce the amount of harmful PAHs produced, they tend to be expensive. In 2006, the International Energy Agency commented on using ESPs to reduce submicron particles but such devices were very expensive and not a ffordable for residential use [27].

Another review suggested the easiest way to control emissions is to use a high quality fuel with low ash content, low moisture, and constant piece size whose options may also not cost competitive, or boilers must use proper combustion chamber designs and adequate air pollution control technology [54]. Therefore, there is a need to develop cost sensitive, yet e ffective, sub- micron PM reduction technologies. One interesting technology dis- cussed in a review by Lim et al. [77], is the use of a miniature pipe bundle heat exchanger (a technology used in the automobile industry) where particles migrate to the lower temperature surfaces and deposit on the tube walls to remove particles from the flue gas. Other options may also include better combustion designs or controls, such as lambda probes. Lambda probes can detect the oxygen levels and e ffectively modulate the air to fuel ratio. Several studies above indicated as op- timal oxygen levels were reached, less particles were formed and a shift towards larger particle sizes was achieved [2,56,63,78]. Perhaps lambda sensors could be used to favor a combustion condition which reduces the amount of harmful NPs produced. Incomplete combustion, smoldering, and transition conditions are known to favor PAH and black carbon production. Further, when temperatures are low, PAHs can condense or adsorb onto particles [77].

Smaller NPs are known to carry larger PAH molecules and are di fficult to remove, while larger more coarse particles carry lower molecular weight PAHs [77]. Likewise, Ghiassi et al. found the most reactive soot had an amorphous nanostructure which was composed of short in- dividual layer planes with no orientation relative to each other [79]. The laboratory study by Hata el al. indicated biomass type and the heating rate had a signi ficant e ffect on the water soluble OC fraction and the smaller the NP, the more water soluble OC the particle con- tained [22]. Very few studies have looked at the microstructure of NPs but this could also provide important information on the NPs reactivity. The microstructure of NPs can give information about particle forma- tion, condensation, coagulation [65,80,81] and the ability to accumu- late reactive substances [65,82]. Ideally, a NP with a low mobility is desired to reduce inhalation or atmospheric risks. Ultimately, it is important to understand the rate of environmentally induced changes and how the migration of particles changes their properties [76]. Understanding the aggregation behavior under both atmospheric and aquatic conditions may help further pre- dict their potential interactions with the ambient environment [26]. Mavrocordatos et al.

[18] investigated the a ffect salt content within the particles play and found their morphology was signi ficantly a ffected in aqueous environments. Perhaps if a su fficient amount of information was gathered on NPs soot emissions from RWC which included explicit details on fuel type, operating parameters, and sampling conditions, manufacturers and operators could be informed with a ‘best practices ’ procedure. As shown in many of the studies reviewed herein, NPs account for a substantial amount of the particle emissions associated with biomass combustion. However, standards enforced by regulatory agencies are mass concentration based, focusing on size ranges less than or equal to 10 µm (total PM; PM T) or less than or equal to 2.5 µm (PM 2.5). Due to R. Trojanowski, V. Fthenakis Renewable and Sustainable Energy Reviews 103 (2019) 515–528 525 NPs small size, current measures may not be appropriate for particles in the nano and ultra fine size fraction since they contribute very little to the overall mass. However, they contribute signi ficantly to the overall number of the airborne particles present [11,83] and, potential adverse health e ffects posed by NPs may go unknown [19]. Lim et al.

[77], reported that dilution sampling a ffects particle emissions by promoting nucleation but results in an increase in the formation of ultra fine par- ticles which are better represented by particle number measurements. Torvela et al. investigated the intermittent period when switching from one condition to another, finding the properties of the PM emissions varied signi ficantly even within a short period suggesting that an eva- luation of environmental and adverse health e ffects based on average particle property values can be misleading [21]. Further, Lamberg et al. concluded from their study that PM 1 mass does not re flect all of the variation affecting possible toxic properties of fine particles originating from combustion [9]. From the Gaegauf et al. [56] study in particular, the highest con- centration of total suspended particles (TSP) (mg/m 3) correlated nicely to the highest total number of nanoparticles ( < 600 nm) collected per MJ of output. Masonry stoves had the highest TSP concentration along with the highest emission factor of NPs per MJ. In comparison, auto- matic feed pellet boilers had the lowest TSP and the lowest total number emission factor of NPs.

However, when looking at the emission factor (mg/MJ) for both TSP and NPs data in detail, the group noticed while each appliance type typically showed good correlation between the two values, individual cases such as the cordwood boiler showed roughly a 40% reduction in the NP emission factor from the TSP emission factor. This supports the suggestion to modify existing test method regulations or add to them a measurement involving particle count, size, or surface area. One positive note from a study which compared vehicle emissions to RWC emissions suggests wood smoke may be associated with less ne- gative health e ffects as diesel NPs were smaller in diameter and have 41% more surface area [64]. Unfortunately another study found PAH content was higher for combustion particles from wood smoke com- pared to vehicle exhaust, causing risk for a high mutagenic and carci- nogenic potential [65]. 8. Conclusions and recommendations Current emission regulations from wood combustion devices in the US and EU are based on an overall mass concentration of particles and NPs are neither measured nor re flected in these emission regulations, allegedly because of their low mass contribution. This review revealed that NPs account for a substantial amount of particle emissions asso- ciated with residential wood combustion (RWC) devices.

A long standing argument has been the need to modify existing test method regulations or add to them a measurement involving particle count, type size, or surface area. NPs from RWC cause local environmental impacts and potential global impacts due to large concentrations in the atmosphere. This review identi fied combustion conditions that may result in increasing amounts of NP emissions. These are associated with the device type, its operation, and the fuel used. We often see an inverse relationship between the total PAH mass and its NP fraction. It is re- ported that PAH emissions could be up to 100 times higher if a stove was not operated properly, although NP production would be de- creased. Also it is reported that, if an advanced system's heating load is decreased, cordwood and automatic wood- fired boilers (pellet and chips) may have trouble modulating, causing them to cycle frequently and generate more mass PAH emissions, but lower NPs. It is a cause for concern that NPs may be undetected as by virtue of their large surface to volume ratio they adsorb larger amounts of reactive compounds and, therefore, may induce a more pronounced pro-in flammatory response than larger particles of the same compound. A signi ficant, and un- expected finding is that as conventional units are displaced by modern, more e fficient and “cleaner” systems, an increase in released NPs may follow.

However, with more e fficient boiler systems PAH levels are being decreased; causing one to argue what is more important NPs or PAHs? Particle distribution of batch-wise fired appliances (wood stoves) varied significantly during a burn cycle, while wood log and continuous fed boilers showed a fairly constant particle size distribution. These differences are likely to in fluence the biological e ffects induced by wood smoke particles and therefore it has been recommended to ex- plore how combustion conditions in fluence the particle properties, their possible health risks, and reactivity within the environment. Although a lot of work has been done to understand the health e ffects associated with RWC NPs, but little is known about the environmental fate of RWC NPs and their e ffect on climate. In addition, NP emission data from wood burning processes under real-world operating conditions are lacking. More data are needed about source, expected quantities or concentrations, and environmental pathways to help identify situations which may be more favorable than others. Several studies show results of size characterization but mor- phology and chemical composition data are limited.

Predicting or studying the aggregation, agglomeration, dispersion, size, solubility, surface area, charge, and composition are all necessary parameters to better predict the environmental fate and any health concerns of bio- mass combustion NPs. While biomass is often considered and en- couraged as a renewable energy source, it is important to not ignore consequences of poor combustion practices and NP production. Several articles have suggested pathways to reduce NPs such as emission control strategies or higher quality fuel sources. Emission control devices suggested for large biomass boilers include ESPs and condensing heat exchangers but their e ffectiveness in controlling NP has not been assessed. Acknowledgement Rebecca Trojanowski is grateful to New York State Energy Research and Development Authority (NYSERDA) for partial support of this re- search through contracts # 29697 and # 63038, Dr. Barbara Panessa- Warren (Guest Scientist at Brookhaven National Laboratory), Dr. Thomas Butcher (Group Leader of the Energy Conversion Group at Brookhaven National Laboratory), and Dr. John B. Warren (Scientist in the Instrumentation Division at Brookhaven National Laboratory). References [1] Buzea C, Pacheco II, Robbie K. Nanomaterials and nanoparticles: sources and toxicity. Biointerphases 2007;2(4):MR17 –71.

[2] Hugony F, Ozgen S, Morreale C, Signorini S, Cernuschi S, Maggioni A, et al. Nanoparticles size distribution in wood combustion. In: Proceedings of the 16th ETH-conference on combustion generated nanoparticles, Zurich, Switzerland; 2012. [3] Saarnio K. Chemical characterisation of fine particles from biomass burning. Kelsinki: Finnish Meteorological Institute; 2013 . [4] Boman BC, Forsberg AB, Jarvholm BG. Adverse health e ffects from ambient air pollution in relation to residentail wood combustion in modern society. Scand J Work Environ Health 2003;29(4):251 –60. [5] Clean Heat- Environmental Action Germany. Residential wood burning: environ- mental impact and sustainable solutions. Berlin: DeutscheUmwelthilfe; 2016 . [6] Chen L-WA, Moomuller H, Arnott WP, Chow JC, Watson JG, Susott RA, et al. Emissions from laboratory combustion of wildland fuels: emission factors and source pro files. Environ Sci Technol 2007;41:4317 –25. [7] (NESCAUM). Northeast States for coordinated air use management. New York State wood heat report: an energy, environmental, and market assessment. Rep. no. 15–26. New York State Energy Research and Development Authority, Albany. [8] Kumar P, Robins A, Vardoulakis S, Britter R. A review of the characteristics of na- noparticulates in the urban atmosphere and the prospects for developing regulatory controls. Atmos Environ 2010;44:5035 –52.

[9] Lamberg H, Nuutinen K, Tissari J, Ruusunen J, Yli-Pirila P, Sippula O, et al. Physiochemical characterization of fine particles from small-scale wood combus- tion. Atmos Environ 2011;45:7635 –43. [10] Bølling AK, Pagels J, Yttri KE, Barregard L, Sallsten G, Schwarze PE, et al. Health effects of residential wood smoke particles: the importance of combustion condi- tions and physicochemical particle properties. Part Fibre Toxicol 2009;6(29) . [11] Hosgood HD, Lan Q, Vermeulen R, Wei H, Reiss B, Coble J, et al. Combustion- R. Trojanowski, V. Fthenakis Renewable and Sustainable Energy Reviews 103 (2019) 515–528 526 derived nanoparticle exposure and household solid fuel use in Xuanwei and Fuyuan, China. Int J Environ Health Res 2012;22(6):571 –81. [12] Nienow AM, Roberts JT, Zachariah MR. Surface chemistry of nanometer-sized aerosol particles: reactions of molecular oxygen with 30 nm soot particles as a function of oxygen partial pressure. J Phys Chem B 2005 . [13] Dellinger B, D'Alessio A, D'Anna A, Ciajolo A, Gullett B, Henry H, et al. Combustion byproducts and their health e ffects: summary of the 10th International congress. Environ Eng Sci 2008;25(8) . [14] Bystrzejewska-Piotrowska G, Golimowski J, Urban PL. Nanoparticles: their poten- tial toxicity, waste and environmental management. Waste Manag 2009;29:2587–95. [15] Somasundaran P, Fang X, Ponnurangam S, Li B.

Nanoparticles: characteristics, mechanisms, and modulation of biotoxicity. KONA Power Part J 2010;28:38 –49. [16] Nowack B, Bucheli TD. occurrence, behavior and e ffects of nanoparticles in the environment. Environ Pollut 2007;150:5 –22. [17] Posfai M, Gelencser A, Simonics R, Arato K, Li J, Hobbs PV, et al. Atmospheric tar balls: particle from biomass and biofuel burning. J Geophys Res 2004;109 . [18] Mavrocordatos D, Kaegi R, Schmatloch V. Fractal analysis of wood combustion aggregates by contact mode atomic force microscopy. Atmos Environ 2002;no. 36:5653–60. [19] Biswas P, Wu C-Y. Nanoparticles and the environment. J Air Waste Manag Assoc 2005;55(6):708–46. [20] Popovicheva OB, Kozlov VS, Engling G, Diapouli E, Persiantseva NM, Timofeev MA, et al. Small-scale study of Siberian biomass burning: I. Smoke microstructure. Aerosol Air Qual Res 2015;15:117 –28. [21] Torvela T, Tissari J, Sippula O, Kaivosoja T, Leskinen J, Viren A, et al. E ffect of wood combustion conditions on the morphology of freshly emitted fine particles. Atmos Environ 2014;87:65 –76. [22] Hata M, Chomanee J, Thongyen T, Bao L, Tekasakul S, Tekasakul P, et al. Characteristics of nanoparticles emitted from burning of biomass fuels. J Environ Sci 2014;28:1913 –20. [23] D'Anna A. Combustion-formed nanoparticles. Proc Combust Inst 2009;32:593 –613.

[24] Caserini S, Galante S, Ozgen S, Cucco S, Gregorio KD, Moretti M. A methodology for elemental and organic carbon emission inventory and results for Lombardy region, Italy. Sci Total Environ 2013;450 –451:22–30. [25] Smita S, Gupta SK, Bartonova A, Dusinska M, Gutleb AC, Rahman Q. Nanoparticles in the environment: assessment using the casual diagram approach. Environ Health 2012;11:1–11. [26] Chen C, Huang W. Aggregation kinetics of diesel soot nanoparticles in wet en- vironments. Environ Sci Technol 2017;51:2077 –86. [27] International Energy Agency. IEA bioenergy updated 21. Biomass Bioenergy 2006;30(3):I–. [28] Jonnalagadda S, Nenzou B. Studies on arsenic rich mini dumps: I. E ffect of the surface soil. J Environ Sci Health 1996;31(8):1909 –15. [29] Siegenthaler J. Hydronics for high e fficiency biomass boilers. NYSERDA; 2017. [30] Twin Waters Energy. Central Boiler (R) Classic Outdoor Wood Furnaces. Twin Waters Energy; 2017. Available online: 〈http://www.twinwatersenergy.com/ howitworks.htm〉. [31] Johansson LS, Leckner B, Gustavsson L, Cooper D, Tullin C, Potter A. Emission characteristics of modern and old-type residential boilers fired with wood logs and wood pellets. Atmos Environ 2004;38:4183 –95. [32] HyProTherm. HyProTherm Outdoor Wood Furnace. HyProTherm Furnace, 6 10 2016.

Available online: 〈http://www.outdoorwoodfurnaceboiler.com/Best- Outdoor-Wood-Furnace-PRINT.html〉. [33] Wood Heating Solution. Forced Air Furnaces. Wood Heating Solutions LLC; 2017. Available online: 〈https://www.wood-heating-solutions.com/outdoor-forced-air- furnaces/〉. [34] United State Environmental Protection Agency, Burn wise: choosing wood burning appliances; May 2017. Available online: 〈https://www.epa.gov/burnwise/ choosing-wood-burning-appliances〉. [Accessed May 2017]. [35] Jensen W, Fremer K, Sierila P, Wartiowaara V. The chemistry of bark. In: The chemistry of wood. Interscience Publishers, NY; 1963. p. 587 –666. [36] Romero C. Tree responses to stem damage. Gainesville: Dept. of Botany, University of Florida; 2006 . [37] Yang Y, Yamauchi H, Nasserzadeh N, Swithenbank J. E ffects of fuel devolatilisation on the combustion of wood chips and incineration of simulated municipal solid wastes in a packed bed. Fuel 2003;82(18):2205 –21. [38] Demirbas A. Combustion characteristics of di fferent biomass fuels. Prog Energy Combust Sci 2004;30(2):219 –30. [39] McKendry P. Energy production from biomass (part 1): overview of biomass. Bioresour Technol 2002;83(1):37 –46. [40] Sawidis T, Breuste J, Mitrovic M, Pavlovic P, Tsigaridas K. Trees as bioindicator of heavy metal pollution in three European cities. Environ Pollut 2011:3560 –70. [41] Alakangas E.

European standards for fuel specifi cation and classes of solid biofuels. In: Solid biofuels for energy, Springer; 2011, p. 21 –41. [42] High Quality Wood Pellets Come in All Sizes and Colors. woodpellets.com. ; 2017. Available online: 〈http://www.woodpellets.com/heating-fuels/pellet-differences. aspx〉. [43] Nilsson D, Bernesson S, Hansson P-A. Pellet production from agricultural raw ma- terials- a systems study. Biomass Bioenergy 2011;35(1):679 –89. [44] European Pellet Council. Handbook for the certi fication of wood pellets for heating purposes: ENplus. European Pellet Council; 2013 . [45] United States Department of Energy. Wood and pellet heating. Available online: 〈https://energy.gov/energysaver/wood-and-pellet-heating〉. [Accessed 2017]. [46] Rinne S, Holmberg H, Myllymaa T, Kontu K, Syri S. "Wood chip drying in con- nection with combined heat and power or solar energy in Finland. In: Proceedings of the EPJ Web of Conferences, vol. 79, no. T3 – Energy Production, Distribution and Storage; 2014. p. 1 –9. [47] Loria K. Watching wood dry. BIOMASS Magazine, 26 July 2016. Available online: 〈http://biomassmagazine.com/articles/12181/watching-wood-dry〉. [Accessed 2017]. [48] Ioannidi M. Woodchip fuel supply chain: from forest to Hopper. Glasgow: Department of Mechanical Engineering at The University of Strathclyde in Glasgow; 2002. [49] Grover P, Mishra S.

Biomass briquetting: technology and practices. Bangkok: Food and Agriculture Organization of the United Nations; 1996 . [50] Shuma R, Madyira DM. Production of loose biomass briquettes from agricultural and forestry residues. Procedia Manuf 2017;7:98 –105. [51] Chin Chin O, Siddiqui KM. Characteristics of some biomass briquettes prepared under modest die pressures. Biomass Bioenergy 2000;18(3):223 –8. [52] Chou C-S, Lin S-H, Lu W-C. Preparation and characterization of solid biomass fuel made from rice straw and rice bran. Fuel Process Technol 2009;90(7 –8):980–7. [53] Ozgen S, Caserini S, Galante S, Giugliano M, Angelino E, Marongiu A, et al. Emission factors from small scale appliances burning wood and pellets. Atmos Environ 2014;94:144 –53. [54] Villeneuve J, Palacios JH, Savoie P, Godbout S. A critical review of emissions standards and regulations regarding biomass combustion in small scale units. Bioresour Technol 2012;111:1 –11. [55] Tissari J, Lyyranen J, Hytonen K, Sippula O, Tapper U, Frey A, et al. Fine particle and gaseous emissions from normal and smouldering wood combustion in a con- ventional masonry heater. Atmos Environ 2008;42:7862 –73. [56] Gaegauf C, Wieser U, Macquat Y. "Field investigation of nanoparticle emissions from various biomass combustion systems. In: International seminar: aerosols from biomass combustion, Zurich, Switzerland; 2001.

[57] Nussbaumer T. "Characterisation of particles from wood combustion with respect to health relevance and electrostratic precipitation. In: Central European Biomass Conference, Gratz, Austria; 2011. [58] Schmatloch V, Brenn J. Fine particle emissions from combustion in small wood fired furnaces. In: International Seminary: Aerosols from Biomass Combustion, Zurich, Switzerland; 2001. [59] McDonald JD, Zielinska B, Fujita EM, Sagebiel JC, Chow JC, Watson JG. Fine particle and gaseous emission rates from residential wood combustion. Environ Sci Technol 2000;34:2080 –91. [60] Orasche J, Seidel T, Hartmann H, Schnelle-Kreis J, Chow JC, Ruppert H, et al. Comparison of emissions from wood combustion. Part 1: emission factors and characteristics from di fferent small-scale residential heating appliances considering particulate matter and polycyclic aromatic hydrocarbon (PAH)-related toxicological potential. Energy Fuels 2012;26:6695 –702. [61] Bologa A, Paur H-R, Seifert H, Woletz K. Fine particle generation, evolution and control by small biomass combustion. Manag Environ Qual: Int J 2012;23(1):36 –55. [62] Hays MD, Smith ND, Kinsey J, Dong Y, Kariher P. Polycyclic aromatic hydrocarbon size distribution in aerosols from appliances of residential wood combustion as determined by direct thermal desportion- GC/MS. J Aerosol Sci 2003;34:1061 –84.

[63] Hueglin C, Gaegauf C, Kunzel S, Burtscher H. Characterization of Wood Combustion Particles: morphology, Mobility and Photoelectric Activity. Environ Sci Technol 1997;31:3439–47. [64] Kocbach A, Johansen B, Schwarze P, Namork E. Analytical electron microscopy of combustion particles: a comparison of vehicle exhaust and residential wood smoke. Sci Total Environ 2005;346:231 –43. [65] Kochbach A, Li Y, Yttri KE, Cassee FR, Schwarze PE, Namork E. Physicochemical characterisation of combustion particles from vehicle exhaust and residential wood smoke. Part Fibre Toxicol 2006;3(1):1 –10. [66] Heckman F. Microstructure of carbon black. Rubber Chem Technol 1964;37(5):1245–98. [67] Corsini E, Ozgen S, Papale A, Galbiati V, Lonati G, Fermo P, et al. Insights on wood combustion generated proin flammatory ultra fine particles (UPF). Toxicol Lett 2017;266:74–84. [68] Commodo M, Sgro LA, D'Anna A, Minutolo P. Size distribution of nanoparticles generated by a heating stove burning wood pellets. EQA-Environ Qual 2012;8:21 –6. [69] Kaivosoja T, Jalava P, Lamberg H, Viren A, Tapanainen M, Torvela T, et al. Comparison of emissions and toxicological properties of fine particles from wood and oil boilers in small (20 –25 kW) and medium (5 –10 MW) scale. Atmos Environ 2013;77:193–201. [70] Leskinen J, Tissari J, Uski O, Viren A, Torvela T, Kaivosoja T, et al.

Fine particle emissions in three di fferent combustion conditions of a wood chip- fired appliance- particulate physico-chemical properties and induced cell death. Atmos Environ 2014;86:129–39. [71] Dasch J Muhlbaler. Particulate and gaseous emissions from wood-burning fire- places. Environ Sci Technol 1982;16(10):639 –45. [72] Ozgen S, Cernuschi S, Giugliano M. Experimental evaluation of particle number emissions from wood combustion in a closed fireplace. Biomass Bioenergy 2013;50:65–75. [73] Ozil F, Haas F, Trouve G. Size distributions and emission factors of PM1 and PM2.5 during wood combustion in domestic fireplaces. ResearchGate; 2014. [74] Kumar P, Pirjola L, Ketzel M, Harrison RM. Nanoparticle emissions from 11 non- vehicle exhaust sources- a review. Atmos Environ 2013;67:252 –77. [75] Tom T, Griet W, Jan C, Silvia L. Literature review of emissions of modern wood combustion devices and emissions reducing technologies, under real-life conditions. University of Antwerp, Institute of Environmental & Sustainable Development; 2017. [76] Baer DR. Surface Characterization of Nanoparticles: critical needs and signi ficant challenges. J Surf Anal 2011;17(3):163 –9. R. Trojanowski, V. Fthenakis Renewable and Sustainable Energy Reviews 103 (2019) 515–528 527 [77] Lim MT, Phan A, Roddy D, Harvey A.

Technologies for measurement and mitigation of particulate emissions from domestic combustion of biomass: a review. Renew Sustain Energy Rev 2015;49:574 –84. [78] Johansson L, Tullin C, Leckner B. Particulate emissions from small-scale biomass combustion. In: International Seminar: Aerosols from Biomass Combustion, Zurich, Switzerland; 2001. [79] Ghiassi H, Toth P, Jaramillo IC, Lighty JS. Soot oxidation-induced fragmentation: Part 1: the relationship between soot nanostructure and oxidation-induced frag- mentation. Combust Flame 2016;163:179 –86. [80] Ishiguro T, Takatori Y, Akihama K. Microstructure of diesel soot particles probed by electrong microscopy: first observation of inner core and outer shell. Combust Flame 1997;108:231 –4. [81] Lighty J, Veranth J, Saro fim A. Combustion aerosols: factors governing their size and compostion and implications to human health. J Waste Manag Assoc 2000;50:1565–681. [82] Berube K, Jones T, Williamson B, Winters C, Morgan A, Richards R. Physicochemical characterisation of diesel exhaust particles: factors for assessing biological activity. Atmos Environ 1999;33:1599 –614. [83] Andersen ZJ, Wahlin P, Raaschou-Nielsen O, Scheike T, Loft S. Ambient particle source apportionment and daily hospital admissions among children and elderly in Copenhagen. J Expo Sci Environ Epidemiol 2007;17:625 –36. [84] Hartmann H, Turowski P, Kiener S.

Electrostatic precipitators for small-scale wood combustion systems- Results from lab- and field tests. Graz: Central European Biomass Conference; 2011. R. Trojanowski, V. Fthenakis Renewable and Sustainable Energy Reviews 103 (2019) 515–528 528