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Fine particle emissions in three different combustion conditions of a wood chip-fired appliance – Particulate physico-chemical properties and induced cell death
... Importantly, the composition of combustion PM is dependent not only on the source, but also on combustion conditions (McClure et al., 2020;Saleh, 2020). Therefore, even for the same fuel, differences in combustion conditions have been found to induce differences in toxicity of the emitted PM (Bølling et al., 2012;Kim et al., 2019;Leskinen et al., 2014;Tapanainen et al., 2011). In this paper, we aim to shed light on the fundamental physicochemical properties of the organic fraction of combustion PM, their dependence on combustion conditions, and how that translates into different toxicological outcomes. ...
... Several studies have attempted to compare the toxicological effects of emissions from fuels combusted under different regimes using setups such as biomass burners, residential heating equipment, stoves, and pellet boilers (Bølling et al., 2012;Happo et al., 2013;Kim et al., 2018Kim et al., , 2019Kocbach et al., 2008;Leskinen et al., 2014). The results emerging from the different studies, however, point in different directions. ...
... Uski et al. (2014) compared the toxicity of PM from smoldering and efficient combustion in heating appliances and found that, while the PM emitted under smoldering conditions caused greater DNA damage and cell death, those emitted from more efficient combustion were more effective in decreasing metabolic activity and causing oxidative stress. Leskinen et al. (2014) reported that the PM emissions from more efficient wood combustion (higher temperatures) caused more cell death, which they attributed to the high concentrations of ash and metals. Kim et al. (2018) compared the toxicity induced in mice respiratory systems by PM from the combustion of different biomass fuels under smoldering and flaming conditions. ...
Light-absorbing organic particulate matter (PM), or brown carbon (BrC), may constitute an important fraction of combustion PM. Here, we investigate the effect of combustion conditions on the molecular sizes of BrC, their light-absorption properties, and their cytotoxicity. We used toluene in a combustion reactor with highly controlled conditions to produce two different types of BrC under two conditions corresponding to smoldering and near-flaming combustion, with temperatures of 670 °C and 1035 °C, respectively. We performed online measurements of the size distributions and light-absorption properties of the BrC. The BrC produced at 1035 °C was more light absorbing, with an imaginary component of the refractive index at 532 nm (k532) an order of magnitude larger than that of the BrC produced at 670 °C. We also collected samples for offline chemical characterization using laser desorption ionization (LDI) mass spectrometry. The LDI mass spectra showed that the BrC produced at 1035 °C was composed of species with significantly larger molecular sizes than the BrC produced at 670 °C. Using human lung epithelial cells, we conducted in vitro cytotoxicity analysis on the two types of BrC with doses ranging from 3.5 to 136.0 μg of BrC/ml. After 24-h exposure, the viability of the cells was assessed using a WST-8 assay. The cytotoxicity analysis showed that, for both BrC samples, the cells exhibited a clear dose-dependent response with significant BrC cytotoxicity that plateaued at the higher doses. However, while the viability of cells exposed to the BrC produced at 1035 °C reached a minimum of around 65% at the highest dose, the BrC produced at 670 °C proved to be significantly more toxic, with the viability dropping asymptotically to 25%. The results presented here suggest that organic PM of smaller molecular sizes produced under lower temperature, smoldering combustion could be significantly more toxic than those of larger molecular sizes produced under higher temperature, flaming conditions. The use of a single-molecule fuel in a highly controlled combustion setup distinguishes this work from experiments that rely on real-life sources and combustion setups, where different combustion conditions could be occurring simultaneously and clouding the conclusions.
... The retained elements may also form low melting potassium compounds contributing to an increased slagging risk in the bottom ash [24][25][26][27][28]. The influence of the combustion conditions on the emission levels during wood chip combustion was studied extensively [29][30][31][32][33][34][35][36][37][38][39][40][41], CFD simulations were applied [42][43][44][45] and the correlation of wood fuel quality and critical combustion behavior like elevated slagging risk and high emission levels [36,37,[46][47][48][49][50] as well as corrosion [51,52] have been reported frequently. ...
... Thus, a pronounced increase of the CO emissions was recorded with fuel moisture content above 30 wt%, which is the maximum allowed fuel moisture content according to the boiler design of the manufacturer. A clear trend of the drying on the TPM emissions could not be verified though incomplete combustion may contribute to soot formation and thus higher TPM emissions [32,34,49]. ...
... However, these effects could not be isolated and verified with the results from the present combustion tests. Furthermore, varying shares of organic compounds such as soot in the particulate matter which are much higher for incomplete conditions during wood combustion may have also contributed to the recorded TPM emission levels[32,36,[95][96][97]. ...
Within six case studies, different drying and sieving process steps were employed for the removal of adhering soil and other extraneous impurities from wood chips. Consequently, it was systematically investigated to which extent this strategy can be used to jointly mitigate the risk of bottom ash slagging and high pollutant emission levels during combustion in an automatically stoked small-scale boiler. Throughout all combustion tests, slag and emission formation were recorded. Formation of agglomerates in the bottom ash was not observed in the fuel bed. However, fuel processing resulted in an increase of the ash shrinking–softening range up to 230 K indicating a lower slagging risk in the bottom ash. An asymptotic trend for the ash melting temperatures was observed as a function of the molar (Si + P + K)/(Ca + Mg) ratio. It was also found that potassium is less efficiently retained in the bottom ash with lower Si content in the fuel. Lower moisture contents in the wood chips typically resulted in lower CO emissions and higher boiler efficiencies for the investigated range of moisture content. The sieving of the unprocessed wood chips reduced NOx emission levels up to 28%. However, fuel processing did not necessarily reduce the level of particulate matter emissions.
... Sigsgaard et al. (2015), within their position paper, gave broader information on particle size distributions by type, as well as new findings on biomass combustion particle formation and toxicity. Inefficient traditional combustion appliances generate an aerosol mainly composed of carbonaceous compounds, while during efficient combustion conditions particles are mainly formed by ash related material Calvo et al., 2015;Fine et al., 2001;Frey et al., 2009;Kelz et al., 2010;Lamberg et al., 2011a;Leskinen et al., 2014;Orasche et al., 2012;Sippula et al., 2007;Tissari et al., 2008aTissari et al., , 2008bVicente et al., 2015a). This paper critically reviews the extensive literature regarding particulate emissions from biomass combustion for residential heating purposes to give an overview of the present state of knowledge. ...
... Finding suitable tracers for residential biomass combustion is not an easy task due to the complex nature of combustion chemistry, which results in high variability of the particle chemical composition. Data reported in the literature show the influence of several factors, such as the stove design, operating conditions, combustion conditions and biomass fuel burned (Eriksson et al., 2014;Fine et al., 2004;Frey et al., 2009;Jordan and Seen, 2005;Lamberg et al., 2011a;Leskinen et al., 2014;Vicente et al., 2015aVicente et al., , 2015cVicente et al., , 2016Weimer et al., 2008). Soot and organic particles are formed during incomplete combustion in small-scale biomass combustion (Bølling et al., 2009;Obaidullah et al., 2012), while during efficient combustion in modern domestic heating systems, the aerosol is dominated by ash compounds (Kaivosoja et al., 2013;Lamberg et al., 2011a;Leskinen et al., 2014;Orasche et al., 2012;Tissari et al., 2008b) and the carbonaceous content in the particulate mass can be below 1% (Löndahl et al., 2008). ...
... Data reported in the literature show the influence of several factors, such as the stove design, operating conditions, combustion conditions and biomass fuel burned (Eriksson et al., 2014;Fine et al., 2004;Frey et al., 2009;Jordan and Seen, 2005;Lamberg et al., 2011a;Leskinen et al., 2014;Vicente et al., 2015aVicente et al., , 2015cVicente et al., , 2016Weimer et al., 2008). Soot and organic particles are formed during incomplete combustion in small-scale biomass combustion (Bølling et al., 2009;Obaidullah et al., 2012), while during efficient combustion in modern domestic heating systems, the aerosol is dominated by ash compounds (Kaivosoja et al., 2013;Lamberg et al., 2011a;Leskinen et al., 2014;Orasche et al., 2012;Tissari et al., 2008b) and the carbonaceous content in the particulate mass can be below 1% (Löndahl et al., 2008). Table 1 displays the carbonaceous particulate mass fraction obtained in distinct biomass combustion appliances. ...
Residential biomass burning has been pointed out as one of the largest sources of fine particles in the global troposphere with serious impacts on air quality, climate and human health. Quantitative estimations of the contribution of this source to the atmospheric particulate matter levels are hard to obtain, because emission factors vary greatly with wood type, combustion equipment and operating conditions. Updated information should improve not only regional and global biomass burning emission inventories, but also the input for atmospheric models. In this work, an extensive tabulation of particulate matter emission factors obtained worldwide is presented and critically evaluated. Existing quantifications and the suitability of specific organic markers to assign the input of residential biomass combustion to the ambient carbonaceous aerosol are also discussed. Based on these organic markers or other tracers, estimates of the contribution of this sector to observed particulate levels by receptor models for different regions around the world are compiled. Key areas requiring future research are highlighted and briefly discussed.
... Besides NO X emissions, the TPM emissions including PM1 can also be predicted by chemical fuel quality, i.e. by the sum of aerosol forming elements including K, Na, S, Cl, Pb and Zn as long as almost complete gas phase burnout conditions are achieved [7-9, 13, 14]. Emissions of organic carbon play only a minor role in automated, efficient systems [15,16]. Three categories of fuels can be defined at least for PM1 emission (sum of K, Na, Pb and Zn), which are (i) fuels with a low PM1 emission range for index values below 1000 mg/kg (d.b.) as typical for softwood and (ii) a medium PM1 range for index values between 1000 and 10,000 mg/kg (d.b.) such as hardwood, poplar or bark. ...
... Similarly, different boiler settings such as the primary or secondary airflow affect the emission behaviour. Thereby, non-optimal combustion settings may lead to high TPM [16,20]. As a consequence, many boiler producers recommend that wood chip furnaces should always be adapted and adjusted to the respective fuel quality for stable operation, low emission and high efficiency [6]. ...
... In some cases, this difference was statistically significant (WC6, WC9 and WC12). Similar to NO X emissions, the higher TPM emissions in boiler A may be attributed to the different combustion technologies, probably due to better airflow management within the combustion chamber of boiler B [16,20]. For WC6 and WC7, very low TPM emissions of below 0.02 g/m 3 (STP, 13% O 2 ) were achieved indicating good combustion conditions and fulfilling the requirements of the German legislation [2]. ...
The introduction of wood chips into the market for small-scale heating appliances of below 100 kW has become more challenging due to stricter regulations on emission levels for carbon monoxide and particle emission, e.g. in Germany. Therefore, it is important to identify high wood chip qualities that are suitable for failure-free and low-emission combustion. In this investigation, several wood chip assortments produced from stem wood and forest residues were analysed and combusted in up to two different wood chip boilers with a nominal heat capacity of 50 and 99 kW at full load. Some combustion tests were performed at part load (i.e. 30% heat output). Throughout experiments, the emission behaviour was measured (CO, NOX and total particulate matter (TPM)). In total, seven different wood chip assortments were tested in the large boiler, whereas ten wood chip assortments were combusted in the smaller furnace. Wood chips from stem wood are characterized by lower ash contents (0.27–1.05 w%, d.b.), lower nitrogen contents (0.04–0.14 w%, d.b.) and lower aerosol forming elements (379–1075 mg/kg, d.b.) compared to forest residues (A = 0.58–2.05 w%¸ N = 0.13–0.32 w%, aerosols = 728–2199 mg/kg, d.b.). Combustion of stem wood caused lower emissions compared to forest residues at full-load operation. Overall, part-load operation caused higher CO and particle emissions. In addition, increases of fine woody particles lead to increases in CO emissions. The influence of moisture content was more pronounced especially for CO emissions.
... Leskinen et al. [65], as well as Torvela et al. [64] evaluated the physical and chemical properties of PM 1 , and gas emissions. Leskinen et al. [65] evaluated combustion of wood chips in different burning conditions (efficient, intermediate and smoldering). ...
... Leskinen et al. [65], as well as Torvela et al. [64] evaluated the physical and chemical properties of PM 1 , and gas emissions. Leskinen et al. [65] evaluated combustion of wood chips in different burning conditions (efficient, intermediate and smoldering). Gas flow was diluted before PM 1 sampling in order to reduce particle concentration to a measurable level and produce enough sample flow rate in the measuring instruments. ...
... Volatiles combustion is in the flaming phase, and char combustion in the smoldering phase. Generally, there are higher emissions during smoldering combustion, where there is a lack of air for complete combustion [27,65]. ...
Emission factor is a relative measure and can be used to estimate emissions from multiple sources of air pollution. For this reason, data from literature on particulate matter emission factors from different types of biomass were evaluated in this paper. Initially, the main sources of particles were described, as well as relevant concepts associated with particle measurements. In addition, articles about particle emissions were classified and described in relation to the sampling environment (open or closed) and type of burned biomass (agricultural, garden, forest, and dung). Based on this analysis, a set of emission factors was presented and discussed. Important observations were made about the main emission sources of particulate matter. Combustion of compacted biomass resulted in lower particulate emission factors. PM2.5 emissions were predominant in the burning of forest biomass. Emission factors were more elevated in laboratory burning, followed by burns in the field, residences and combustors..
... Fig. 1 Time series of O2, CO, particle number emissions and particle number mean diameters during combustion of bark pellets [10] The levels of O2, CO, particle number mean diameter and emissions clearly shows a fluctuation that has a periodicity of 15-20 min. Familiar pattern was earlier observed by J. Leskinen et al. [11]. These mentioned authors attributes oxygen and incomplete combustion compounds emission instabilities to the fuel feeder and movement of the grate. ...
... It must be defined that X. Zhang et al. [9] also notes that emissions are significantly affected by the excess of air. Second one is that during grate movement a portion of fuel is removed from blocking of primary air inlets (grate bar slits) [11]. ...
Measurements of pollutant concentrations in the flue gases of a biofuel boiler show that pollutants concentrations fluctuate by 10-100% and more at short time intervals. Large fluctuations in concentrations hinder the effective application of pollution reduction measures. During the research, flue gas composition measurements were performed in 4 MW, 8 MW industrial biofuel boilers and 20 kW experimental model. The results of the research showed that the change of CO, NO, NO2, SO2, H2S, O2 and particulate matter concentrations is related to the periodicity of the boiler grate movement. During the movement of the grate, the surface of the fuel bed is mechanically disrupted. The different composition of the fuel layers is mixed and this affects the changes in the concentration of combustion products. The clarity of the concentration fluctuations depends on the emissions, the type of fuel and the combustion parameters.
... The combustion system, air supply and fuel feeding were fully automated. In addition, the reactor included a ceramic insulated combustion chamber, heat exchangers with cooling circuits and a stack with a flue gas fan ( Fig. 2 and Fig. S1) [15,21]. The reactor was operated with commercial and chemically untreated wood chips including both bark and stem composed of spruce (70%) and typical Finnish deciduous tree species (30%). ...
... Fuel input power was 9 kW. The fuel supplier was the same as in the earlier studies and details on the chemical fuel composition, heating values and ash content are reported by Leskinen et al. and Kortelainen et al. [21,22]. ...
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.
... Small and medium-scale biomass heating systems may be good alternatives to heating systems fired with fuel oil because overall the emissions from both small and medium-scale controlled woodfueled heating systems caused fewer cytotoxic effects and DNA damage in a cell model than the emissions from the corresponding oil-fueled heating systems (Kasurinen et al., 2015a). To mitigate the health effects of biomass-derived PM emissions, reduction of exposure to biomass PM emissions through "wise heating", e.g. using appropriate boilers, dry biomass fuels and complete combustion conditions, combined with cleaner biomass fuels producing limited emissions and exhibiting low toxicity is strongly recommended (Fachinger et al., 2017;Kaivosoja et al., 2013;Leskinen et al., 2014). Giant Miscanthus (Miscanthus x giganteus) is a high-yielding perennial grass with the potential to meet biomass fuel production criteria (Atkinson, 2009;Kad ziulien _ e et al., 2014). ...
... In these studies, PAHs were thermally decomposed, resulting in reduced PAH levels in comparison to combustion of straw with a moisture content of about 30 wt% (Lu et al., 2009;Yang et al., 2006). Our results are also in good agreement with the findings reported in other studies showing that wood smoke particles generally contain considerable amounts of PAHs (Dilger et al., 2016;Jalava et al., 2010;Kaivosoja et al., 2013;Leskinen et al., 2014). ...
(https://doi.org/10.1016/j.atmosenv.2017.05.019)
Inhalation of particulate matter (PM) from residential biomass combustion is epidemiologically associated with cardiovascular and pulmonary diseases. This study investigates PM0.4-1 emissions from combustion of commercial Miscanthus straw (MS), softwood chips (SWC) and beech wood chips (BWC) in a domestic-scale boiler (40 kW). The PM0.4-1 emitted during combustion of the MS, SWC and BWC were characterized by ICP-MS/OES, XRD, SEM, TEM, and DLS. Cytotoxicity and genotoxicity in human alveolar epithelial A549 and human bronchial epithelial BEAS-2B cells were assessed by the WST-1 assay and the DNA-Alkaline Unwinding Assay (DAUA). PM0.4-1 uptake/translocation in cells was investigated with a new method developed using a confocal reflection microscope.
... While the Teon lters collected particles >0.22 mm, the collection by ESP favored smaller particle sizes. 66,67 To this end, composition of smaller particles may have enhanced the solubility of photolyzed OA. ESP experiments for lumber OA exhibited an increase in the UV by a factor of 4 and an increase in the visible by a factor of 5.5 ( Fig. S9c and d †) indicating that the residual OA prevented the full representation of lightabsorptive properties of the sample aer photolytic aging. ...
Emissions from large-scale fires significantly contribute to the atmospheric burden of primary organic aerosol (OA). The frequency of fires occurring at the wildland-urban interface (WUI) is increasing, with biomass and...
... Many studies have focused on determining the emission of semivolatile compounds, such as PAHs, for the combustion of conventional fuels (coal, wood) [30][31][32][33]. Considering the limited information on the PAHs content in agricultural biomass ashes, as well as increasing evidence of PAHs presence in the environment, the present study was aimed to determine PAHs content in the cyclone and stack fly ashes from the cigarette combustion facility with soybean straw as a feed fuel. ...
Agricultural biomass is considered a preferred renewable energy source in Serbia because of its availability and suitability to limit the use of fossil fuel resources and reduce greenhouse gas emissions. Therefore, constant work has been done to develop technologies that enable its utilization for energy purposes. As an example of these efforts, in the Agricultural Corporation PKB, the soybean straw cigarette-type combustion system has been applied for greenhouse heating for over a decade. However, many volatile and semivolatile organic compounds are emitted directly into the atmosphere or concentrated in ash particles during agricultural biomass combustion. Since some of the emitted compounds, such as polycyclic aromatic hydrocarbons (PAHs), are toxic, monitoring their concentrations in fly ash is recommended. Literature data regarding PAHs content in agricultural biomass ashes are insubstantial, especially in Serbia. For that purpose, PAHs contents in the cyclone (CB) and stack (SB) fly ashes of soybean straw were investigated and compared. In addition, the emission factors, toxicity, carcinogenicity and benzo[a]pyrene equivalence concentrations were determined and used to estimate the potential environmental impact of these ashes. As a result, SB ash has been shown to have a higher potential environmental risk than CB ash. Hence, an assessment of using soybean straw as a feed fuel in a real cigarette-type combustion plant regarding PAHs emission is given. These results provide important information for optimizing combustion conditions and assisting the local entities in managing air pollution and control policies in Serbia.
... In 2017, 8720 tons of particulate matter 2.5 micron and smaller (PM 2.5 ) were attributed to residential heating in New York (NY), accounting for 79% of PM 2.5 in NY (United States Environmental Protection Agency 2021). Multiple studies have shown that the fine particles and polyaromatic hydrocarbons (PAHs) are toxic for human cells (Jalava et al. 2012;Kaivosoja et al. 2013;Kocbach Bølling et al. 2009;Lamberg et al. 2011;Leskinen et al. 2014). As many as 30 million US residents are impacted by woodsmoke each year (Noonan, Ward, and Semmens 2015;Rogalsky et al. 2014). ...
This study investigated how heat demand and fuel loading affect the emissions from outdoor wood-fired hydronic heaters by testing two such appliances using an integrated-duty cycle test method. This test included transient operating conditions, such as cold and hot-starts and modulation between 15 and 100% of maximum rated output. Emission values indicate transient operating conditions produce higher emissions than steady state operation. Cold starts resulted in elevated particulate matter emission factors for both appliances; in one case the particulate matter emission factor for this period was >3500 mg/MJ, which represented emissions 20 times the average value. Additionally, when heat demand was cycled-elevated CO emission factors were measured, with values >5000 mg/MJ for both appliances and more than 3 times the appliance averages, respectively. It follows that the appliance average particulate matter emission factors and CO emission factors were not representative of the actual EF values during these transient periods. In contrast, methane emission factors were relatively stable throughout all tested combustion conditions; however, they were much higher than oil-fired appliances are therefore should not be ignored. These findings demonstrate that wood-fired hydronic heater emissions during transient operating conditions can be significantly greater than emissions during steady-state test conditions, such as those used in typical certification tests. Consequently, certification test values for particulate matter and CO emission factors may significantly underestimate the actual emissions of these appliances when operated in a home. Use of integrated duty-cycle test protocols that capture cold-starts and reloading are better for representing in-use operations of wood-fired hydronic heaters and provide more realistic emissions and delivered efficiency measurements.Implications: In this work we provide information on the particulate and gaseous emissions from two wood fired outdoor hydronic heaters. The units were tested using an integrated duty cycle test method that captured cold starts, reload, cyclic and modulating periods between 15 and 100% of maximum rated output. The data and results show a much higher emission factor than those reported by current certification test methods but are more representative of how the units operate in the field.
... Khalil and Rasmussen, 2003 [67] argued that a tracer may be considered ideal when certain peculiar characteristics are met: it has to be resistant to degradation, source specific and constant and allow for highprecision measurement. However, some factors, such as the complex chemical combustion conditions, the high inhomogeneity of the particles, the different types of biofuel used, the operating conditions or the formation of ash, can make it difficult to find a tracer that meets all of these characteristics at once [68][69][70][71][72][73][74]. Water-soluble potassium (K + ) has been proposed as a tracer for biomass burning in receptor models due to its ubiquity in the cytoplasm of plants [75], and a strong positive correlation was observed among K + , organic carbon (OC), elemental carbon (EC) and WSOCs (water-soluble organic compounds) that indicated crop residues burning to carbonaceous aerosols [76]. ...
The adverse effects of atmospheric particulate matter (PM) on health and ecosystems, as well as on meteorology and climate change, are well known to the scientific community. It is therefore undeniable that a good understanding of the sources of PM is crucial for effective control of emissions and to protect public health. One of the major contributions to atmospheric PM is biomass burning, a practice used both in agriculture and home heating, which can be traced and identified by analyzing sugars emitted from the combustion of cellulose and hemicellulose that make up biomass. In this review comparing almost 200 selected articles, we highlight the most recent studies that broaden such category of tracers, covering research publications on residential wood combustions, open-fire or combustion chamber burnings and ambient PM in different regions of Asia, America and Europe. The purpose of the present work is to collect data in the literature that indicate a direct correspondence between biomass burning and saccharides emitted into the atmosphere with regard to distinguishing common sugars attributed to biomass burning from those that have co-causes of issue. In this paper, we provide a list of 24 compounds, including those most commonly recognized as biomass burning tracers (i.e., levoglucosan, mannosan and galactosan), from which it emerges that monosaccharide anhydrides, sugar alcohols and primary sugars have been widely reported as organic tracers for biomass combustion, although it has also been shown that emissions of these compounds depend not only on combustion characteristics and equipment but also on fuel type, combustion quality and weather conditions. Although it appears that it is currently not possible to define a single compound as a universal indicator of biomass combustion, this review provides a valuable tool for the collection of information in the literature and identifies analytes that can lead to the determination of patterns for the distribution between PM generated by biomass combustion.
... It increases the partial pressure of CO 2 in the flue gas hence making CO 2 sequestration more economical, moreover, the CO 2 in the flue gas can be recycled for combustion purposes [9]. Additionally, it reduces the pollutants and precursors that cause adverse health complications like lung diseases and mutagenic component in the emissions thought to be cancer causing [10][11][12]. Owing to the effects of particle pollution, study on PM formation, emission and its control has attracted more attention, the combustion gas mixture being crucial as well. ...
... Recently, many studies have investigated the light absorption and chemical characteristics of BB BrC from laboratory-controlled combustion (Hoffer et al., 2016;Park and Yu, 2016;Budisulistiorini et al., 2017). In controlled combustion experiments, combustion conditions play a significantly important role in impacting the light absorption and chemical composition of BrC as they impact the characteristics of combustion products (Leskinen et al., 2014;Park et al., 2020). The common combustion conditions mainly include heating temperature, heating atmosphere, combustion phase, and combustion efficiency. ...
Organic carbon (OC) emitted from biomass burning (BB) plays an important role in the global radiation budget. In this work, primary OC emitted from wood pyrolysis and combustion under nitrogen (N2) and air conditions in a tube furnace was investigated. The absorption spectra, chemical functional groups, and molecular compositions of OC were analyzed using UV-Vis-NIR spectrophotometer, Fourier transform infrared spectroscopy (FTIR), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), respectively. The light absorption properties showed that the mass absorption efficiency at 365 nm (MAE365) of methanol-soluble OC (MSOC) is 3.1-3.8 times higher than that of water-soluble OC (WSOC). Moreover, the MAE365 values derived from the N2 pyrolysis atmosphere are higher than that from the air atmosphere for both MSOC and WSOC. These results indicated that OC extracted by methanol has higher light absorption, especially for the OC emitted from the N2 pyrolysis atmosphere. Although the FTIR spectra showed identical functional groups for the OC from the air and N2 conditions, molecular compositions from the FT-ICR MS analysis presented significant differences. The molecular weight (MW), double bonds equivalent (DBE), DBE/C, and modified aromaticity index (AImod) of extracted OC showed higher values in MSOC than those in WSOC, and higher values under the N2 atmosphere than those under the air atmosphere. In addition, MAE365 showed positive correlations with MW (r = 0.94), DBE (r = 0.88), DBE/C (r = 0.96), and AImod (r = 0.97), whereas negative correlations with H/C (r = -0.97), O/C (r = -0.90), N/C (r = -0.88), and S/C (r = -0.93). These results indicated that molecules with larger MW and a high level of unsaturation and aromaticity present higher light absorption, while molecules with high elemental ratios of H/C, O/C, N/C, and S/C are adverse to light absorption.
... However, they can contain considerable amounts of transition metals, namely zinc [57][58][59] . In cases of just about complete combustion, zinc is the reason behind most of the cytotoxic studies [60][61][62] . Unlike agroforestry biomass, which results in emissions and ash with a higher content of metals, the use of SCG is advantageous due to its low metal concentration in both emissions and ash. ...
Industrial development and increased energy requirements have led to high consumption of fossil fuels. Thus, environmental pollution has become a profound problem. Every year, a large amount of agro-industrial, municipal and forest residues are treated as waste, but they can be recovered and used to produce thermal and electrical energy through biological or thermochemical conversion processes. Among the main types of agro-industrial waste, soluble coffee residues represent a significant quantity all over the world. Silver skin and spent coffee grounds (SCG) are the main residues of the coffee industry. The many organic compounds contained in coffee residues suggest that their recovery and use could be very beneficial. Indeed, thanks to their composition, they can be used in the production of biodiesel, as a source of sugar, as a precursor for the creation of active carbon or as a sorbent for the removal of metals. After a careful evaluation of the possible uses of coffee grounds, the aim of this research was to show a broad characterization of coffee waste for energy purposes through physical and chemical analyses that highlight the most significant quality indexes, the interactions between them and the quantification of their importance. Results identify important tools for the qualification and quantification of the effects of coffee waste properties on energy production processes. They show that (SCG) are an excellent raw material as biomass, with excellent values in terms of calorific value and low ash content, allowing the production of 98% coffee pellets that are highly suitable for use in thermal conversion systems. Combustion tests were also carried out in an 80kWth boiler and the resulting emissions without any type of abatement filter were characterized.
... The laboratory scale fixed bed reactors have also been used to investigate the soot formation in gasification or partial oxidation. Torvela et al. [123] and Leskinen et al. [216] investigated the fine particle emissions in a biomass combustor with consideration of three conditions, i.e. efficient, intermediate and smouldering combustion. Mustafa et al. used the cone calorimeter to study the particulate emissions in rich burning gasification zone [217]. ...
Biomass gasification is a promising technology in current and future low carbon energy systems. Soot formation is a great technical challenge for the industrialization of biomass gasification that is inevitable at high temperature and fuel rich conditions. In this review, a comprehensive summary of soot formation in biomass gasification is provided with special focus on entrained flow technologies. The topics covered the state of the art knowledge of soot formation in different gasifiers, the fundamental knowledge, experimental methods and recent control strategies. Soot generation and oxidation mechanism are discussed while the relationship between soot, tar and char in biomass gasification are analyzed in detail. Reaction models for soot formation coupled to the gasification process are introduced, including (semi-)empirical and detailed models. Effect of biomass components and ash forming elements on soot formation are highlighted. This is followed by a detailed description of in-situ and ex-situ experimental measurements, such as the optical diagnostics, aerosol particle mass analyzer and mass spectrometer. Soot formation characteristics and properties in different types of gasifiers are then addressed in detail with an emphasis of entrained flow gasifiers. Finally, the soot control strategies in biomass gasification are reviewed and evaluated. This review concludes by summarizing the available knowledge and challenges in soot formation during biomass gasification.
... Moisture can cause a bias of the NDIR analyzer up to 30% for NO 2 (i.e., at a wavelength of 6.21 µm), 20% for SO 2 (i.e., at a wavelength of 7.45 µm), and 5% for NO (i.e., at a wavelength of 5.25 µm) [4]. For particulate matter, the particle concentration can be monitored by light scattering analyzers (e.g., optical particle counter or condensation particle counter) [5][6][7][8][9], light absorption analyzers (e.g., spot meters, aethalometer, photoacoustic soot sensor, or laser-induced incandescence) [5,6,10], light extinction analyzers (e.g., cavity ring-down or opacity meter) [5,6,11,12] and microbalance analyzers (e.g., tapered element oscillation microbalance or quartz crystal microbalance) [5,6,13]. Size distributions of particles can be continuously determined using a fast-mobility particle sizer and an electric low-pressure impactor [5,6,[14][15][16]. ...
A continuous emission monitoring system (CEMS) is a well-known tool used to analyze the concentrations of air pollutants from stationary sources. In a CEMS, the presence of a high moisture level in a sample causes a loss of analytes due to artifact formation or absorption. This issue brings about a bias in the measurement data. Thus, moisture removal is an important pretreatment step. Condensation and permeation methods have been widely employed to remove moisture from the CEMS for gaseous compounds. In terms of particulate matter, dilution methods have been applied to reduce the moisture level in the gas stream. Therefore, condensation, permeation, and dilution methods are critically reviewed in this work. The removal efficiencies and recovery rates of analytes are discussed, as well as the advantages and disadvantages of each technique. Furthermore, the suitable applications of each technique are determined. Condensation methods have not been well documented so far, while permeation and dilution methods have been continuously studied. Many types of permeation materials have been developed. The limitations of each method have been overcome over the years. However, the most reliable technique has not yet been discovered.
... The combustion device used herein was a reciprocating grate burner with a nominal fuel power of 40 kW. Details regarding the combustion reactor are presented in an earlier publication [28]. The burner was designed for miscellaneous solid fuels, and in this experiment, mixed wood chips with an average size of 30 × 30 mm from both hardwood and softwood were used as fuel. ...
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.
... Elements accounted for a higher particulate mass fraction during the operation of the woodstove compared to the fireplace (Table S1). The effect of combustion conditions on the particulate matter chemical composition has been reported in several source characterisation studies (Alves et al., 2011a;Calvo et al., 2015;Lamberg et al., 2011;Leskinen et al., 2014). The predominance of K and Ca in wood burning households is in agreement with previous studies (Molnár et al., 2005). ...
The incomplete wood combustion in appliances operated in batch mode is a recognised source of both in- and outdoor airborne pollutants, especially particulate matter (PM). Data on pollutant levels and PM characteristics in households with wood burning devices in developed countries are scarce with most studies describing stove change out programmes or other intervention measures. The aim of the present study was to simultaneously evaluate indoor and outdoor concentrations of CO, CO2 and PM10 during the operation of wood burning appliances (open fireplace and woodstove) in unoccupied rural households. PM10 samples were analysed for water soluble inorganic ions, major and trace elements, organic carbon (OC), elemental carbon (EC), and detailed organic speciation. The CO 8-hour average concentrations did not exceed the protection limit despite the sharp increases observed in relation to background levels. During the open fireplace operation, PM10 levels rose up 12 times compared to background concentrations, while the airtight stove resulted in a 2-fold increase. The inhalation cancer risk of particulate bound PAHs in the room equipped with woodstove was estimated to be negligible while the long-term exposure to PAH levels measured in the fireplace room may contribute to the development of cancer. The excess lifetime cancer risk resulting from the particle-bound Cr(VI) exposure during the fireplace and woodstove operation was higher than 1.0 × 10-6 and 1.0 × 10-5, respectively. Levoglucosan was one of the most abundant individual species both indoors and outdoors. This study underlines air pollution hazards and risks arising from the operation of traditional wood burning appliances.
... The utilization of wood fuels (e.g., wood pellets, wood chips, wood logs) for the provision of heat in small-scale combustion appliances within the residential sector is always associated with particulate matter (PM) emissions harmful to human health and to the environment [1][2][3][4]. Compared to wood combustion processes realized in largescale heating or CHP plants for e.g. the provision of district heat, smallscale household combustion devices cause typically higher PM emissions as these conversion units are commonly not equipped with secondary removal techniques (e.g., baghouse filter, electrostatic precipitator) due to economic reasons [5,6]. Furthermore, small-scale wood combustion frequently tends to show incomplete combustion behavior as these appliances have typically only limited possibilities to control the combustion conditions in a highly sophisticated way [7]. ...
The objective of this study is to analyze the influence offive different additives (i.e., kaolinite, anorthite, calciumsilicate, titanium dioxide, and aluminum hydroxide) in the lab-scale to estimate their suitability for (inorganic)particulate matter (PM) emission reduction of beech wood chips during small-scale combustion. Therefore, ashesatfive different temperatures (i.e., 550 °C, 700 °C, 900 °C, 1000 °C, and 1100 °C) are produced for each biomass-additive-mixture and analyzed with respect to their potassium content and potassium recovery rate being ty-pically the most important PM component. Additionally, the crystalline fractions of the ash samples are analyzedby X-ray diffraction to allow for conclusions on the potassium retention ability of the used additives. Finally,thermogravimetric analyses are conducted for the obtained 550 °C ashes in addition to the ash analysis. Byevaluating and assessing the analytical results for the different biomass-additive-samples, the additives kaolinite,anorthite, and aluminum hydroxide are identified as the most promising ones with respect to the potentiallyachievable inorganic PM reduction during the small-scale wood chip combustion.
... However, the composition of the PM 1 size fraction in FPBO combustion also differs from that in wood combustion (Fig. 2). In wood-fired boilers, PM 1 fine fly ash is dominated mainly by alkali metal sulphates, chlorides and carbonates and to a smaller extent by zinc Leskinen et al., 2014), while in the FPBO boiler studied, PM 1 contained several additional refractory elements, particularly Ca, Mg, Mn, Fe and Al. This is likely explained by the higher combustion temperature in FPBO combustion when compared to wood combustion. ...
There is currently great interest in replacing fossil-oil with renewable fuels in energy production. Fast pyrolysis bio-oil (FPBO) made of lignocellulosic biomass is one such alternative to replace fossil oil, such as heavy fuel oil (HFO), in energy boilers. However, it is not known how this fuel change will alter the quantity and quality of emissions affecting human health. In this work, particulate emissions from a real-scale commercially operated FPBO boiler plant are characterized, including extensive physico-chemical and toxicological analyses. These are then compared to emission characteristics of heavy fuel-oil and wood fired boilers. Finally, the effects of the fuel choice on the emissions, their potential health effects and the requirements for flue gas cleaning in small-to medium-sized boiler units are discussed.
The total suspended particulate matter and fine particulate matter (PM1) concentrations in FPBO boiler flue gases before filtration were higher than in HFO boilers and lower or on a level similar to wood-fired
grate boilers. FPBO particles consisted mainly of ash species and contained less polycyclic aromatic hydrocarbons (PAH) and heavy metals than had previously been measured from HFO combustion. This feature was clearly reflected in the toxicological properties of FPBO particle emissions, which showed less acute toxicity effects on the cell line than HFO combustion particles. The electrostatic precipitator used in the boiler plant efficiently removed flue gas particles of all sizes. Only minor differences in the toxicological properties of particles upstream and downstream of the electrostatic precipitator were observed, when the same particulate mass from both situations was given to the cells.
... To obtain an almost dry probe, the emulsions were combined and predried within a rotary evaporator at 35°C and 150 mbar. The remaining liquid was removed using an air stream of air mixed with nitrogen (see [29,30]). In order to be able to use the particulate matter in the bacterial contact test (BCT) and the umu test, a concentration of 5 mg/mL 2 was set from the dried particles in deionized water. ...
Many studies showed that there are associations between particulate matter (PM) emissions and negative health effects. Sources for particulate matter PM emissions are, in addition to industry and traffic, residential wood combustion. Such PM emissions consist typically of non-combustible impurities contained naturally within the wood fuels (e.g., ash). Additionally, heavy metals from the wood fuel and/or polycyclic aromatic hydrocarbons (PAHs) formed during incomplete combustions may condense on the surface of these particulate matter and may increase the toxicity of these particles. To reduce negative health effects, wood combustion appliances are forced to emit less PM emissions. This may lead to an increased use of electrostatic precipitators to meet the valid threshold values. Against this background, the overall goal of this paper is it to compare biological effects of PM emissions released under full- and partial-load conditions of a wood pellet boiler with and without a flue gas treatment with an electrostatic precipitator in bacterial assays. The results show that PM emissions emitted under full-load conditions show a lower cytotoxic potential than those collected under partial load. No difference for the genotoxicity between full-load and partial-load conditions could be identified. However, significantly lower genotoxicity during full-load operation and precipitation but higher genotoxicity during partial load and precipitation have been found. Conclusively, the results indicate that the PM emissions emitted under full-load conditions show overall less cytotoxicity and genotoxicity than the emissions from partial-load operation. The PAH concentration doubles between full load and partial load with separator and quadruples between full load and partial load without precipitator.
... Chemical properties of diesel and biomass particles, produced under controlled laboratory conditions, have been associated with the presence of K and Ca content for biomass particles, and Al, Ca and Zn for diesel particles (Longhin et al., 2016). K and Zn were clearly the most abundant metals found in the ash emission from biomass burning using wood chips ( Leskinen et al., 2014). According to Torvela et al. (2014b) the cell toxic potential of wood combustion is likely caused by specific metal species such as Zn, when the mass of carbonaceous species in the PM is minor. ...
The ceramics manufacturing in northeastern Brazil has been dominated by archaic procedures, in which the consumption of native wood extracted from the natural Caatinga biome is used as fuel in the process of clay burning. The aims of this study were to assess particulate matter (PM) physico-chemical characteristics and atmospheric modeling analyses, as well as the genotoxic potential using Tradescantia micronucleus assay associated to the emissions from the ceramic industry complex. The average PM concentration for all analyzed periods was 65 ± 26.2 μg m ⁻³ for total suspended particles, and 23.4 ± 19.9 μg m ⁻³ for PM 10 . Furthermore, the morphological analysis showed particles typical from biomass burning, such as soot carbon, spherical organic carbon and inorganic ash. The major elemental components were identified as Ba, Zn, Al, K, and Ca. Enrichment factor values showed that Ba and Zn were highly enriched in the ceramic production areas. Modeling analysis suggested that these particles can reach regions farther away from the emission sources. The frequency of micronuclei was 2.7–7.2 times higher than in the non-exposed area for all analyzed months. Moreover, a negative correlation between micronucleus and wind speed (r = −0.91; p = 0.04) was verified. This study addressed the effects of PM emitted from the ceramic industry on DNA damage and showed its genotoxic effects in meiotic cells despite the PM 10 concentrations being within the upper WHO limits. The particulate air pollutants emitted from the wood burning by ceramics manufacturing are able to induce DNA damage in T. pallida, suggesting a required higher control of these air pollution emissions.
... PAHs have been reported to be emitted in large amounts during biomass combustion, and significantly higher PAH emissions from softwood than those from hardwood have been observed. Several studies have shown that combustion conditions can influence PAH emissions, and several authors have observed that emissions from traditional appliances may be up to 145 times higher than those observed for automatic stoves Vicente and Alves 2018;Gonçalves et al. 2011;Leskinen et al. 2014). Half-life of atmospheric PAHs varies from hours to weeks, and after emissions (Fig. 1). ...
Polycyclic aromatic hydrocarbons (PAHs) are worldwide pollutants produced mainly during incomplete combustion and pyrolysis of organic substances. PAH derivatives are components with hydrogen on the aromatic ring substituted by carbonyl-, nitro- and hydroxyl-functional groups (N-PAH, O-PAH or OH-PAH), or a group of heterocyclic PAHs containing one sulfur atom in place of a carbon atom in the aromatic ring. PAHs and their derivatives can be either introduced in the atmosphere directly in this form as primary pollutants, or formed by homogenous and heterogeneous oxidation reactions. During the last decades, interest on studying PAH derivatives has increased because derivatives may be more harmful than parent compounds. PAH derivatives have been detected in the atmospheric particulate matter in numerous cities worldwide. PAH derivatives enter living organisms by inhalation, oral ingestion and dermal contact. In vivo and in vitro experiments together with epidemiological studies have shown the toxic effects of PAH derivatives, notably for compounds present in airborne and diesel exhaust particles. Here we review the sources, the mechanisms of formation, the physicochemical properties, the analytical methods, and the toxicological effects of PAHs and their derivatives in airborne particulate matter.
... Many factors influence the emissions from residential combustion, such as the type (and conditions) of fuel, the type of equipment (Johansson et al. 2004), the air supply and the burning habits Hellén et al. 2008;Leskinen et al. 2014;Tissari et al. 2008;Vicente et al. 2015). Emission inventories for this specific sector should always (when possible) take into account the different equipment and its combustion conditions, even when reported as sector-total for final purposes. ...
Usually, annual emission data from residential combustion sector are spatially disaggregated by population density to the sub-municipality spatial level. The aim of the present work is to define a methodological approach to develop/build a high-resolution emission inventory from residential combustion following a bottom–up approach. The conceptual model considers different approaches by fuel category (solid fuel–wood, gas and liquid fuels) according to distinct spatial coverage and type of activity data available for each category. For solid fuels, detailed activity data (per district), disaggregated according to the number and type of equipment, burned wood species and consumption rate, as well as specific emission factors (per wood species) were used. With regard to the gas and liquid fuels, the total national emission by fuel type using national consumption data and broader emission factors was disaggregated to the sub-municipality scale based only on the number of heating equipment. The choice of these disaggregation factors was influenced by both data availability and relevance. The results of the new disaggregated emission data have been compared with emission values resulting from the classical top–down approach using census/population data. The selected case study is Portugal. The results pointed out that major differences exist when comparing both approaches, namely regarding the spatial distribution/allocation of emissions. In the new approach, emissions are more redistributed over the territory, while in the old distribution, emissions are concentrated in the coastal urban areas (with hotspots in the main urban areas of Porto and Lisbon).
... Pb, Cr, Hg, and Cd) and various toxic gases (e.g., the toxic dioxins, furans) [6][7][8] . Many studies have shown that these directly emitted particles from crop residue, wood, and solid waste combustion harm human health and affect climate change by altering direct radiative forcing or acting as cloud condensation nuclei (CCN) to influence indirect radiative forcing [9][10][11][12] . Moreover, the oxidation of gaseous precursors further contributes to the formation of secondary particles 13,14 . ...
Morphology, composition, and mixing state of individual particles emitted from crop residue, wood, and solid waste combustion in a residential stove were analyzed using transmission electron microscopy (TEM). Our study showed that particles from crop residue and apple wood combustion were mainly organic matter (OM) in smoldering phase, whereas soot-OM internally mixed with K in flaming phase. Wild grass combustion in flaming phase released some Cl-rich-OM/soot particles and cardboard combustion released OM and S-rich particles. Interestingly, particles from hardwood (pear wood and bamboo) and softwood (cypress and pine wood) combustion were mainly soot and OM in the flaming phase, respectively. The combustion of foam boxes, rubber tires, and plastic bottles/bags in the flaming phase released large amounts of soot internally mixed with a small amount of OM, whereas the combustion of printed circuit boards and copper-core cables emitted large amounts of OM with Br-rich inclusions. In addition, the printed circuit board combustion released toxic metals containing Pb, Zn, Sn, and Sb. The results are important to document properties of primary particles from combustion sources, which can be used to trace the sources of ambient particles and to know their potential impacts in human health and radiative forcing in the air.
... These therefore include also traditional systems, such as woodstoves and fireplaces, whose emissions are known to be particularly high [27]. Nevertheless, modern wood chip plants are characterised by lower emission values [28], although not yet comparable with the emissions from natural gas boilers (see Table 1). ...
The use of wood biomass as a fuel for domestic and industrial heating systems allows for a reduction of CO2 emissions at a global scale, but it may also result in worse local air quality conditions, due to their emissions of particulate matter. The aim of this study is to assess the actual trend of atmospheric pollution in a study area, assuming that all heating systems are replaced by small size biomass boilers linked to the buildings through district heating network. Ground level concentrations of particulate matter, emitted by different heating systems, are therefore evaluated through numerical simulations performed by means of an atmospheric dispersion model (Sirane). As a first step, we have compared the environmental impact of a woodchip boilers network with that given by the use of traditional heating systems, i.e. wood stoves and natural gas boilers. As a second step, we have analysed the impact of such a network taking into account different emission scenarios, related to different boilers operating conditions. Results show that the environmental performances of a woodchip boilers network can be optimized by combining it with other renewable sources of energy devoted to the supply of hot water. The adopted analysis methodology can be applied to other real or hypothetic punctual sources on the territory.
... The combustion experiments were performed in a laboratory environment using a pellet boiler (Biotech GmbH, with 25 kW nominal output. The gaseous emissions (40 relevant calibrated compounds, e.g., CO, NO x , and CO 2 ) were measured continuously directly from the stack during PM sampling by a Fourier Transform Infrared analyzer (FTIR, Gasmet) as described in more detail in Leskinen et al. (2014). ...
Nanomaterials (NM) exhibit novel physicochemical properties that determine their interaction with biological substrates and processes. Recent nano-technological advances are leading to wide usage of metallic nanoparticles (NPs) in various fields. However, the increasing use of NPs has led to their release into environment and the toxicity of NPs on human health has become a concern. Moreover, there are inadvertently generated metallic NPs which are formed during various human activities (e.g. metal processing and energy production). Unfortunately, there are still widespread controversies and ambiguities with respect to the toxic effects and mechanisms of metallic NPs, e.g. metal oxides including ZnO.
... With stem-wood-based pellets, the size distribution variations as the function of time were very minor, whereas with peat and bark fuels and their mixtures, both particle number concentrations and particle sizes increased during the grate movement (Fig. 3). The effect of the grate movement in a reciprocating grate burner system has been previously studied in detail in the laboratory, which suggests that the grate movement caused an increase in the gasification rate of the fuel, which can lead to incomplete oxidation of gases and the formation of soot particles [34]. ...
In view of the tremendous emissions of toxic gases and particulate matter (PM) by low-power firewood-fueled fireplaces, there is an urgent need for effective measures to lower emissions to keep this renewable and economical source for private home heating available in the future. For this purpose, an advanced combustion air control system was developed and tested on a commercial fireplace (HKD7, Bunner GmbH, Eggenfelden, Germany), complemented with a commercial oxidation catalyst (EmTechEngineering GmbH, Leipzig, Germany) placed in the post-combustion zone. Combustion air stream control of the wood-log charge combustion was realized by five different control algorithms to describe all situations of combustion properly. These control algorithms are based on the signals of commercial sensors representing catalyst temperature (thermocouple), residual oxygen concentration (LSU 4.9, Bosch GmbH, Gerlingen, Germany) and CO/HC-content in the exhaust (LH-sensor, Lamtec Mess- und Regeltechnik für Feuerungen GmbH & Co. KG, Walldorf (Germany)). The actual flows of the combustion air streams, as calculated for the primary and secondary combustion zone, are adjusted by motor-driven shutters and commercial air mass flow sensors (HFM7, Bosch GmbH, Gerlingen, Germany) in separate feedback control loops. For the first time, the residual CO/HC-content (CO, methane, formaldehyde, etc.) in the flue gas is in-situ monitored with a long-term stable AuPt/YSZ/Pt mixed potential high-temperature gas sensor, which allows continuous estimation of the flue gas quality with an accuracy of about ±10%. This parameter is not only an essential input for advanced combustion air stream control but also provides monitoring of the actual combustion quality and logging of this value over a whole heating period. By many firing experiments in the laboratory and by field tests over four months, it could be demonstrated that with this long-term stable and advanced automated firing system, depression of the gaseous emissions by about 90% related to manually operated fireplaces without catalyst could be achieved. In addition, preliminary investigations at a firing appliance complemented by an electrostatic precipitator yielded PM emission depression between 70% and 90%, depending on the firewood load.
This study investigates the transferability of aluminum-silicate-based fuel additivation as a primary, fuel-based mitigation measure for inorganic alkali-based particulate matter (PM) emissions during the complete combustion of wood chips. Therefore, wood chips are additivated with 0.5 wt% of three different types of the aluminum-silicate-based additive kaolin, which differ mainly in their particle size distribution, and with one type of kaolinite. The subsequent combustion trials with non-additivated and additivated wood chips are carried out in a small-scale combustion plant. To evaluate the effect of the additivation of the wood chips, the total particulate matter (TPM) emissions, the potassium (K) emissions, the ultra-fine PM emissions and the carbon monoxide (CO) emissions, as well as the chemical composition of the resulting ashes, are analyzed. In order to compare the primary, fuel-side mitigation measure of fuel additivation with the established secondary mitigation measures, an electrostatic precipitator (ESP) is additionally utilized. The respective result shows that the aluminum-silicate-based fuel additivation of the wood chips with kaolin and the use of the ESP lead to comparable reductions in the TPM emissions, as well as the share of the ultra-fine particle fraction in the PM emissions. The addition of the additive kaolin additionally causes the significant mitigation of the K and CO emissions. Overall, the obtained results suggest that the combined utilization of fuel-side aluminum-silicate-based fuel additivation, together with the secondary mitigation measure of the ESP, might be very promising to further reduce PM emissions from combustion devices that operate with wood chips.
An electrostatic precipitator (ESP) is a quite efficient device to remove fly ash from small-scale solid fuel combustions. Under corona discharge, the gaseous medium becomes ionised, and particles get charged, colliding with ions. The electric field forces charged particles to remove from gases as well as induces the movement of generated ions, causing the secondary electrohydrodynamic flow. Thus, the particle charge, presence of neighbour particles, ESP electric field and gas flow turbulence can enhance particle coagulation. Therefore, the ultrafine particle concentration in ESP is expected to evolute under electrostatic removal and enhanced coagulation. In the present work, the contribution of coagulation is reasoned and confirmed by experimental measurements carried out at the ESP used to control emissions from a 160-kW boiler with biomass combustion. ESP was operated in several operating modes to ensure different coagulation conditions. The changes in the particle concentrations were measured with two techniques simultaneously. It was found that coagulation can be responsible for up to 5% removal efficiency depending on ESP operation parameters. The present work can promote a deeper understanding of the processes in electrostatic precipitation, and obtained results can be helpful in practical ESP engineering.
Wood is a renewable fuel, however the combustion of wood can lead to significant dust emissions. The application of fabric filters is one possibility to ensure low particulate matter emissions. Nevertheless, these filters are so far not used for small-scale firing systems. In this work, the mitigation potential of a newly developed fabric filter concept with pulse-jet regeneration, based on a stainless-steel mesh was studied. The filter was tested on a commercially available 24 kW biomass boiler, which was operated with wood pellets and wood chips. Experiments showed a linear dependency of the separation efficiencies and clean gas concentrations on average pressure drop while a logarithmic dependency of the clean gas concentrations on an empirical factor k was proven. The filter showed good regenerability and dust separation efficiencies up to 83 % and 90 % during combustion of wood pellets and wood chips. The pulse-jet regeneration showed a short-time peak of dust emissions behind the filter which can represent between 24 and 60 % of the total dust emissions during a whole filtration cycle. Nevertheless, the application of different filters with 25 and 50 μm mesh size guarantees an efficient dust removal. In a first phase during filter cake formation, the concentrations can exceed the limit value, but once a filter cake had built up, the concentrations drop drastically below 0.01 g m⁻³. In summary, the filters show good regenerability and efficient dust separation and thus further development potential.
The main technical characteristics of the electrostatic precipitation process, which can be applied to ESPs of any type, are the electric field strength and the Nt-product (the product of ion concentration and the residence time of the particle in the electric field). The present study investigates the impact of these characteristics on the efficiency of ESP in suppressing particulate matter (PM) emissions from a 160-kW boiler with wood pellet combustion. PM concentration was reduced to 2 mg/m³, representing a removal efficiency of ∼95%. The SMPS continuously recorded changes in the particle concentration. The growth of removal efficiency was not uniform with enhancing ESP parameters. The study shows that Nt-product demonstrated a prior effect on removal efficiency until growing up to the value of 4.5×10¹⁴ s/m³. Exceeding this value of Nt-product had no significant impact on the cleaning efficiency, but the electric field became prior. The results of the present research can help to optimise the ESP dimension parameters, therefore they can be used in the practical engineering of any new ESP to collect ultrafine particles and promote the implementation of ESPs for small-scale boilers for global pollution.
Le besoin de combustibles alternatifs aux énergies fossiles a conduit à se tourner vers de nouveaux combustibles renouvelables. La biomasse est l’une des alternatives les plus utilisées. La biomasse peut être classée en fonction de son origine, comme la biomasse de bois qui est actuellement la plus utilisée. Il existe d’autres types de biomasse comme celle reposant sur les plantations énergétiques. Cependant, l’exploitation de cette biomasse alternative n’est pas toujours correcte et on sait qu’une mauvaise utilisation peut engendrer des comportements différents dans les appareils de combustion avec des conséquences en termes d’émissions polluantes. C’est pourquoi nous devons étudier l’effet de la nature et de la composition de la biomasse sur ses émissions lors de la combustion. Afin d’étudier expérimentalement la combustion de la biomasse, un banc expérimental basé sur une chaudière domestique à granulés de 20kW a été mis en place pendant la thèse. Les trois biomasses utilisées pour cette thèse sont le bois, le miscanthus et la paille. Les entrées d’air et de combustible sont contrôlées, le banc est instrumenté et permet des mesures d’émissions polluantes gazeuses et particulaires. De nombreux équipements sont utilisés pour le prélèvement (FPS) et les mesures d’émissions polluantes ont été mises en place (TESTO, SMPS, PPS, ELPI, TEOM). Des mesures de masse volumique effective des particules produites pendant la combustion de la biomasse ont également été réalisées. Différents paramètres tels que le mode d’alimentation (pulsé ou continu), la distribution d’air au sein du foyer et la nature de la biomasse sont étudiés. Les résultats obtenus ont montré que les émissions de CO sont fortement influencées par le type d’alimentation de la chaudière. Nous avons réussi à réduire d’environ 40 % les émissions de CO d’un chauffage classique en modifiant simplement son mode d’alimentation. La distribution d’apport en air dans le foyer de combustion a un effet important sur la réduction des émissions polluantes gazeuses. Les résultats obtenus ont montré de nettes différences dans les niveaux d’émissions gazeuses des trois types de biomasse, le bois étant le moins émissif. Enfin, Au niveau des émissions des particules par les trois types de biomasse, il y a des différences la concentration en masse et la distribution de taille des particules. Les images MET et la masse volumique spécifique montrent des différences entre les particules produites par le miscanthus comparées à celles produites par le bois.
The present study investigates methods for predicting the efficiency of electrostatic precipitation for controlling particulate matter (PM) emissions from small-scale heating units, namely, solid fuel combustion boilers with heating power output less than 300 kW. The prediction correctness for particle precipitation efficiency is considered on the basis of the accuracy of the estimated charge on a particle. Prediction of the specific PM from small-scale boilers requires a relevant model of specified particle charging. Three appropriate particle charge models have been used to predict the efficiency of a specific electrostatic precipitator (ESP). The prediction results are compared on the basis of experimental measurements taken from an ESP used to control the emissions from a 160-kW boiler. The measurements are based on different physical principles and are undertaken simultaneously. The optimal method for particle charge evaluation is determined to allow the practical modeling of an ESP to control the PM emissions from small-scale units with solid fuel combustion.
The important sources of air pollution can be identified with the installation of ambient air quality monitoring station. The sampling with monitoring station can provide current status of air quality of that particular area. This chapter describes the different measuring and analytical technique for monitoring of air quality. The different method for the collection of pollutant is also explained. The types of the gaseous monitoring techniques were described in Sects. 2.3 and its subsections. The different measurement techniques of particulate pollutants were explained in Sects. 2.4. The Section 2.5 explained some of the important concepts of data quality assurance and quality control (QA/QC) with reference to the analysis of vapour-phase chemical composition in air.
Small-scale heating units with solid fuels combustion cause a global atmospheric pollution by fine particles. Electrostatic precipitation is suggested as a method of controlling fine particle emissions. The correctness of modelling for precipitation efficiency is defined by the accuracy of the evaluation of particle charges. This work focuses on reviewing the existing particle charging theories in terms of their suitability for practical engineering for the electrostatic precipitation of fly ash particles from the flue gases of small-scale boilers. Charging calculation methods were rated as a function of the particle sizes, external discharge electric field strength, and ion density-time product and compared to published experimental data. Two particle charge rating methods were identified to be suitable for the electrostatic precipitation of such particles.
The Ministry of the Environment of the Czech Republic within the Operational Programme Environment of the European Union (EU) has supported a ‘grant to replace old boilers’ from 2015 to 2020. The aim was to replace outdated, non-ecological, solid-fuel boilers with modern low-emission boilers (for the combustion of biomass, coal, or a combination), heat pumps, gas boilers, or solar systems. All heat sources must comply with the Ecodesign Directive of the EU. According to the Air Protection Act in the Czech Republic, commencing in 2022, outdated boilers of the 1st and 2nd emission classes will no longer be operable in households. The grant also aimed to reduce particulate matter (PM), organic gaseous compounds, and CO and NOx emissions.
Our goal was to compare the PM emissions of four boilers: an outdated overfire boiler (B1), an outdated boiler with down-draft combustion (B2), a new gasification boiler (B3), and a new automatic boiler (B4). A Dekati low-pressure cascade impactor was used to determine the mass concentration of individual dust fractions; a scanning mobility particle sizer SMPS 3936 was utilized to determine the particle size distributions of the dust particles. Dry and wet spruce wood and wood pellets were combusted.
Regarding the mass concentration of the PM and specific emissions (SE) of individual size fractions, they were much higher in boilers of older types (B1 and B2), while the reduction in SE of PM was very significant in boilers of newer types (B3 and B4). However, the SE of ultrafine particles (PM0.1) from the newer boilers remained in a range similar to that of B1 at Pmin and B2.
Abstract. Residential wood combustion (RWC) emits large amounts of gaseous and particulate organic aerosol (OA). In the atmosphere, the emission is transformed via oxidative reactions, which are under daylight conditions driven mainly by hydroxyl radicals. This continuing oxidative aging produces secondary OA and may change the health- and climate-related properties of the emission. In this work, emissions from two modern residential logwood combustion appliances were photochemically aged in an oxidation flow reactor with various OH exposure levels, reaching up to 6 × 1011 s cm<sup>−3</sup> (equivalent to one week in the atmosphere). Gaseous organic compounds were analysed by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), while particulate OA was analysed online by an aerosol mass spectrometer (AMS) and offline by thermal-optical analysis and thermal desorption-gas chromatography mass spectrometry. Photochemical reactions increased the mass of particulate organic carbon by a factor of 1.3–3.9. The increase in mass took place during the first atmospheric equivalent day of aging, after which the enhancement was independent of the extent of photochemical exposure. However, aging increased the oxidation state of the particulate OA linearly throughout the assessed range, with ∆H:C/∆O:C slopes between −0.17 and −0.49 in van Krevelen space. Aging led to an increase in acidic fragmentation products in both phases. For the volatile organic compounds measured by PTR-ToF-MS, the formation of small carbonylic compounds combined with the rapid degradation of primary volatile organic compounds such as aromatic compounds led to a continuous increase in both the O:C and H:C ratios. Overall, the share of polycyclic aromatic compounds (PACs) in particles degraded rapidly during aging, although some oxygen-substituted PACs, most notably naphthaldehydic acid, increased, in particular during relatively short exposures. Similarly, the concentrations of particulate nitrophenols rose extensively during the first atmospheric equivalent day. During continuous photochemical aging, the dominant reaction mechanisms shifted from the initial gas phase functionalisation/condensation to the transformation of the particulate OA by further oxidation reactions and fragmentation. The observed continuous transformation of OA composition throughout a broad range of OH exposures indicates that the entire atmospheric lifetime of the emission, from fresh to shortly aged to long-term aged emission (representative of long-range transported pollutants), needs to be explored to fully assess the potential climate and health effects of OA emissions.
The aim of this study was to investigate the use of an electrostatic precipitator (ESP) for controlling the emissions of particulate matter (PM) from small-scale heating units, specifically boilers that combust solid fuel with a heating power output of <300 kW. The equilibrium between the required precipitation efficiency and the structural parameters of the ESP in combination with the applied voltage were determined. This study presents a method of optimising the applied voltage alongside the specific ESP structural parameters while retaining the required precipitation efficiency. The ESP was designed, optimised, and integrated into a 15-kW boiler without expanding its volume. The theoretically predicted voltages and resulting ESP efficiency (20 kV and 85% respectively) were verified by measuring the reduction in the particle number concentration. The measurements were based on different principles and simultaneously sampled. The PM concentrations were reduced below 40 mg/m³ (0 °C, 101.3 kPa; at reference O2 = 10 %vol.) by nominal and reducing the heat power, which allowed the boiler to meet the requirements of the EU’s Ecodesign Directive. The presented optimisation method can be used in the practical engineering of any type of ESP.
Residential wood combustion (RWC) is a major source of climate-impacting emissions, like short-lived climate forcers (SLCF) and biogenic CO2, in Finland. In this paper, we present projections for those emissions from 2015 to 2040. We calculated the climate impact of the emissions using regional temperature potential metrics presented in literature. In our results, the climate impacts are given as global and Arctic temperature responses caused by the studied emissions in a 25 year time span. The results show that SLCF emissions from RWC cause a significant warming impact. Using our selected metrics, SLCF emissions from RWC added to the warming impact of Finland's projected greenhouse gas emissions by 28% in global temperature response and by 170% in Arctic response. When compared with other common heating methods in Finnish detached houses, using a typical Finnish stove (masonry heater) was the least climate-friendly option. Taking biogenic CO2 emissions into account further highlighted this finding. Finally, we assessed the change in climate impact when implementing various emission reduction measures for RWC. With a time span of 25 years, early action was found to be even more crucial than the eventual reductions in annual emissions in 2040.
The increased use of wood as a heating fuel in residential and small commercial buildings has increased concern about potential environmental and safety impacts, specifically particulate matter (PM) emissions in the nanometer range. Larger particles (> 2.5 µm) can be effectively removed from exhaust streams by emission control devices. However, nanoparticles (NP), due to their size, are more difficult to capture in exhaust flue gases. In addition, NPs have a higher surface to volume ratio, allowing them to absorb organic compounds, causing them to be more reactive than their larger counterparts. This review focuses on the NPs produced from residential wood heating devices. Current emission regulations do not reflect the NP count or type produced from residential wood combustion, although most published studies show that a significant portion of the particles produced during combustion is in the nano-size range. Fuel type, device type and combustion periods have all shown to impact, at various degrees, the NPs produced. Contrary to common expectations, it appears that modern units may generate a higher count of NPs, although emitting less particulate mass than older units. This investigation supports arguments of needed particle type and count regulations in addition to the current mass based emission regulations. In addition to a critical review and analysis, recommendations are made regarding future testing, monitoring and environmental impact studies that address the significance of NP emissions.
Designs of ‘improved’ stoves are introduced recently to benefit the solid fuel consumption of cooking activities in developing countries, but the uncertainties concerning the combustion processes and particulate emissions remain to be poorly characterised. To help understand this, combustion in three examples of ‘improved’ African cookstoves was investigated in the laboratory. A typical European heating stove was included for comparison purpose. Detailed aerosol emissions were studied in real-time with an Aerosol Mass Spectrometer and Single Particle Soot Photometer, to explore interactions between black carbon (BC) and organic carbon aerosols, which were parameterised according to modified combustion efficiency (MCE), a common metric used within the atmospheric emission community. Greater than 50% of the total organic matter (OM) was found in BC-containing particles when MCE was > 0.95 for dry oak and coal fuels, whereas at lower MCE, over 80% of the total OM for most of the fuels existed in particles without detectable BC. When the OM mass fraction of total particulate matter (PM1) > 0.9, the mass ratio of OM to refractory BC in BC-containing particles was about 2-3, but only ~0.8 when OM mass fraction < 0.9. These findings are not currently included in models and such information should be considered in the future emission scenarios.
Increasing public concern regarding air quality has led to the development of efficient aerosol-monitoring techniques. Among the various aerosol measurement instruments based on electrical methods, in this study, an electrical cascade impactor (ECI) was designed and fabricated in our laboratory and was used to measure the real-time size distribution of submicron-sized aerosols. In the study by Park et al. (2007), it was assumed that the size distribution of incoming particles follows a unimodal lognormal distribution. However, in this study, the distribution of particles captured at each stage (including the Faraday cage) was assumed to be a unimodal lognormal distribution; hence, the incoming particles may follow any size distribution. After the particle charging characteristics were obtained for different particle sizes, experiments were performed with monodisperse test particles to determine the collection efficiency of each stage. The current measured in each stage was converted into a number based size distribution of aerosols by using the data inversion algorithm, which utilized the experimentally obtained collection efficiency. Then, a performance evaluation was performed, both in the laboratory and in the field. The results obtained by our ECI were in agreement with the scanning mobility particle sizer (SMPS) data.
Four different domestic heating boilers and four types of fuel (lignite, wet wood, wood pellets and mixed fuel) were tested, and the emissions of the particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) were correlated. Dekati low-pressure impactor (DLPI, Dekati) sorting of the PM fractions into PM0.1, PM1, PM2.5 and PM10 was used to determine the emission factors of the PAHs in a dilution tunnel via isokinetic sampling and was compared with a cyclone (Tecora). The 4 PAHs were mostly detected on the fine particles of PM1 in the DLPI and on the fine particles of PM2.5 in the cyclone, and in some cases, they were mainly detected in polyurethane foam (PUF) used for the collection of the gas phase placed behind the DLPI and cyclone. The effectiveness of DLPI sampling was generally comparable or lower than the cyclone sampling of the range 0.01–1.33 mg kg–1.
In this paper, results on the potential toxicity of ultrafine particles (UFPs d < 100 nm) emitted by the combustion of logwood and pellet (hardwood and softwood) are reported. The data were collected during the TOBICUP (TOxicity of BIomass COmbustion generated Ultrafine Particles) project, carried out by a team composed of interdisciplinary research groups. The genotoxic evaluation was performed on A549 cells (human lung carcinomacells) using UFPs whose chemical composition was assessed by a suite of analytical techniques. Comet assay and γ-H2AX evaluation show a significant DNA damage after 24 h treatment. The interpretation of the results is based on the correlation among toxicological results, chemical-physical properties of UFPs, and the type and efficiency conditions in residential pellet or logwood stoves.
Two common types of wood (beech and fir) were burned in commercial pellet (11.1 kW) and wood (8.2 kW) stoves following a combustion cycle simulating the behavior of a real-world user. Ultrafine particulate matter (UFP, dp < 100 nm) was sampled with three parallel multistage impactors and analyzed for metals, main water soluble ions, anhydrosugars, total carbon, and PAH content. The measurement of the number concentration and size distribution was also performed by a fourth multistage impactor. UFP mass emission factors averaged to 424 mg/kgfuel for all the tested stove and wood type (fir, beech) combinations except for beech log burning in the wood stove (838 mg/kgfuel). Compositional differences were observed for pellets and wood UFP samples, where high TC levels characterize the wood log combustion and potassium salts are dominant in every pellet sample. Crucial aspects determining the UFP composition in the wood stove experiments are critical situations in terms of available oxygen (a lack or an excess of combustion air) and high temperatures. Whereas for the automatically controlled pellets stove local situations (e.g., hindered air-fuel mixing due to heaps of pellets on the burner pot) determine the emission levels and composition. Wood samples contain more potentially carcinogenic PAHs with respect to pellets samples. Some diagnostic ratios related to PAH isomers and anhydrosugars compiled from experimental UFP data in the present study and compared to literature values proposed for the emission source discrimination for atmospheric aerosol, extend the evaluation usually limited to higher particle size fractions also to UFP.
Five different boiler types (automatic boiler, over-fire boiler, boiler with down-draft combustion, two types of gasification boiler) representing residential scale combustion technology were tested in this study. Boilers were fueled with various fuels (lignite, wet and dry wood, wood pellets, mixed fuel) and the combustion emissions were measured both at nominal output and reduced output. The investigated emissions comprised CO, OGC and PM. A cyclone and a low-pressure impactor were used for the determination of PM emissions. It was found that the emission factors for CO, OGC and PM depend more on the boiler type and mode of operation (reduced or nominal output) than on the fuel type. Data from the DLPI show that in most cases, PM1 represents approximately 80 % of the total PM mass. PM0.1 represents 15 – 30 % (modern boilers) or 5 – 10 % (old type boilers) of the total PM mass. A comparison of the results shows that the emission factors for PM obtained by cyclone were higher than the emission factors obtained using a DLPI.
Equipment consisting of annular denuders, a filter, and a polyurethane foam adsorbent was used for sampling 15 PAHs from the diluted emission from a heat-storing masonry heater. The denuder method was compared to the ISO 11338 method which was used for the sampling from hot and undiluted exhaust gas. The denuder method used with the exhaust dilution gave a realistic gas-particle distribution of PAHs in more atmospheric-like conditions compared to the sampling from undiluted exhaust gas where PAHs were almost totally in the gas phase. The results gained with the denuder method from the diluted exhaust are more relevant, e.g., from exposure and atmospheric processes point of view. The emissions from smoldering combustion conditions (SC) were compared with the emissions from normal combustion conditions (NC). The emission of each PAH was 7 to 14 times higher from SC than from NC, and the gas-particle distribution was shifted towards the particle phase due to increased condensation of PAHs. The PAHs could be divided into three groups based on their phase distributions. In the first group, PAHs existed mostly in the gas phase in both combustion cases; the vapor pressures of PAHs were lower than the saturation vapor pressures. In the second group, the gas phase was saturated and the concentration was almost the same in both combustion cases, whereas the particle phase concentration was higher in SC. In the third group, PAHs were mostly in the particle phase where the concentration was higher in SC.
Primary fine particulate matter (PM2.5) emissions from low-altitude sources, such as traffic and domestic combustion, may cause immediate exposure near the source. In this paper we present emission estimate and uncertainty analysis of PM2.5 emissions from the vehicular traffic and domestic wood combustion sectors. Our estimate of national PM2.5 emissions in 2000 from domestic wood combustion was 7.6 Gg a(-1) and that from vehicular traffic, including non-exhaust emissions, 5.8 Gg a(-1). These values correspond to 25% and 19% of the national total PM 2.5 emissions, respectively. The uncertainties were high for non-exhaust traffic and domestic wood combustion emissions, 37% down, 53% up and 36% down, 50% up of the mean value (95% confidence interval limits), respectively. For traffic exhaust emissions, the uncertainties were lower, 11% down, 13% up. Uncertainties in the domestic combustion emission factors were the most important individual parameters accounting for total uncertainty.
Inflammation is regarded as an important mechanism behind mortality and morbidity experienced by cardiorespiratory patients exposed to urban air particulate matter (PM). Small-scale biomass combustion is an important source of particulate air pollution. In this study, we investigated association between inflammatory responses and chemical composition of PM(1) emissions from seven different small-scale wood combustion appliances representing old and modern technologies. Healthy C57Bl/6J mice were exposed by intratracheal aspiration to single dose (10 mg/kg) of particulate samples. At 4 and 18 h after the exposure, bronchoalveolar lavage fluid (BALF) as well as serum was collected for subsequent analyses of inflammatory indicators (interleukin (IL)-6, IL-1β, IL-12, and IL-10; tumor necrosis factor-α (TNF-α); keratinocyte-derived chemoattractant (KC), and interferon-γ (IFN-γ)) in multiplexing assay. When the responses to the PM(1) samples were compared on an equal mass basis, the PM from modern technology appliances increased IL-6, KC, and IL-1β levels significantly in BALF at 4 and 18 h after the exposure. In contrast, these responses were seen only at 4 h time point in serum. Increased cytokine concentrations correlated with metal-rich ash related compounds which were more predominant in the modern technology furnaces emissions. These particles induced both local and systemic inflammation. Instead, polycyclic hydrocarbon (PAH) rich PM(1) samples from old technology (OT) evoked only minor inflammatory responses. In conclusion, the combustion technology largely affects the toxicological and chemical characteristics of the emissions. The large mass emissions of old combustion technology should be considered, when evaluating the overall harmfulness between the appliances. However, even the small emissions from modern technologies may pose significant toxic risks.
Particle emissions from a turbo-charged diesel off-road engine were characterized with DMA + CNC and electron microscopy for comparison of different sampling and dilution systems. Four different sampling methods were used: (1) two ejector diluters, (2) partial flow and ejector diluter, (3) porous tube and ejector diluter, and (4) porous tube diluter. Number size distributions for partial flow and ejector dilution had modes at 25–30 nm and at 45–50 nm independent of the dilution ratio. The mode at 25–30 nm indicated nucleation during dilution in these experiments and was clearly most significant for the partial flow and ejector diluter setup. This was attributed to the temperature difference between exhaust gas, sample line, and partial flow diluter and cold dilution air. For other dilution systems the main mode was at 45 nm and indications of a mode at 15–20 nm were observed depending on the dilution ratio. Especially for the porous tube diluter, the main mechanism for particle growth was condensation on the surfaces of the existing particles. According to this study the best dilution system for obtaining a number size distribution without any significant nucleation effects was the porous tube dilution setup.
There is a growing industry fabricating products that are based on nanoparticles (particle diameter dp≤100 nm). The production of these particles requires detection, classification and characterisation of even smaller particles because of, e.g. preventing unwanted particle emissions from the processes and health issues. Monitoring of the processes is needed on one hand for product quality determinations, on the other hand to ensure safe and particle-free working conditions. Thus simple, fast and reliable measurement devices are needed for particle characterisation.
Several studies have shown that combustion-derived fine particles cause adverse health effects. Previous toxicological studies on combustion-derived fine particles have rarely involved multiple endpoints and a detailed characterization of chemical composition. In this study, we developed a novel particle sampling system for toxicological and chemical characterization (PSTC), consisting of the Dekati Gravimetric Impactor (DGI) and a porous tube diluter. Physico-chemical and toxicological properties of the particles emitted from various combustion sources were evaluated in two measurement campaigns. First, the DGI was compared with the High-Volume Cascade Impactor (HVCI) and to the Dekati Low-Pressure Impactor (DLPI), using the same dilution system and the same sampling conditions. Only small differences were observed in the mass size distributions, total particulate matter (PM), and particulate matter with diameter smaller than 1 um (PM(1)) concentrations and geometric mass mean diameters (GMMD) between these three impactors. Second, the PSTC was compared with the HVCI sampling system, which has been optimal for collection of particulate samples for toxicological and chemical analyses. Differences were observed in the mass size distributions, total PM and PM(1) emissions, and GMMDs, probably due to the different sampling and dilution methods as well as different sampling substrates which affected the behavior of semi-volatile and volatile organic compounds. However, no significant differences were detected in the in vitro measurements of cytotoxicity between the samples collected with the PSTC and the HVCI systems. In measurements of genotoxicity, significant differences between the two sampling systems were seen only with the particles emitted from the sauna stove. In conclusion, due to compact size, PSTC is an applicable method for use in particle sampling as part of the toxicological and chemical characterization of particulate emissions from different combustion sources. It offers some advantages compared to the previously used high-volume sampling methods including compactness for field measurements, simple preparation of sample substrates and high extraction efficiency.
The last decade has seen tremendous advances in atmospheric aerosol particle research that is often performed in the context of climate and global change science. Biomass burning, one of the largest sources of accumulation mode particles globally, has been closely studied for its radiative, geochemical, and dynamic impacts. These studies have taken many forms including laboratory burns, in situ experiments, remote sensing, and modeling. While the differing perspectives of these studies have ultimately improved our qualitative understanding of biomass-burning issues, the varied nature of the work make inter-comparisons and resolutions of some specific issues difficult. In short, the literature base has become a milieu of small pieces of the biomass-burning puzzle. This manuscript, the second part of four, examines the properties of biomass-burning particle emissions. Here we review and discuss the literature concerning the measurement of smoke particle size, chemistry, thermodynamic properties, and emission factors. Where appropriate, critiques of measurement techniques are presented. We show that very large differences in measured particle properties have appeared in the literature, in particular with regards to particle carbon budgets. We investigate emissions uncertainties using scale analyses, which shows that while emission factors for grass and brush are relatively well known, very large uncertainties still exist in emission factors of boreal, temperate and some tropical forests. Based on an uncertainty analysis of the community data set of biomass burning measurements, we present simplified models for particle size and emission factors. We close this review paper with a discussion of the community experimental data, point to lapses in the data set, and prioritize future research topics.
Associations have been found between day-to-day particulate air pollution and increased risk of various adverse health outcomes, including cardiopulmonary mortality. However, studies of health effects of long-term particulate air pollution have been less conclusive.
To assess the relationship between long-term exposure to fine particulate air pollution and all-cause, lung cancer, and cardiopulmonary mortality.
Vital status and cause of death data were collected by the American Cancer Society as part of the Cancer Prevention II study, an ongoing prospective mortality study, which enrolled approximately 1.2 million adults in 1982. Participants completed a questionnaire detailing individual risk factor data (age, sex, race, weight, height, smoking history, education, marital status, diet, alcohol consumption, and occupational exposures). The risk factor data for approximately 500 000 adults were linked with air pollution data for metropolitan areas throughout the United States and combined with vital status and cause of death data through December 31, 1998.
All-cause, lung cancer, and cardiopulmonary mortality.
Fine particulate and sulfur oxide--related pollution were associated with all-cause, lung cancer, and cardiopulmonary mortality. Each 10-microg/m(3) elevation in fine particulate air pollution was associated with approximately a 4%, 6%, and 8% increased risk of all-cause, cardiopulmonary, and lung cancer mortality, respectively. Measures of coarse particle fraction and total suspended particles were not consistently associated with mortality.
Long-term exposure to combustion-related fine particulate air pollution is an important environmental risk factor for cardiopulmonary and lung cancer mortality.
Unlabelled:
A summary of a critical review by a working group of the German commission on Air Pollution Prevention of VDI and DIN of the actual data on exposure and health effects (excluding cancer) of fine particulate air pollution is presented.
Exposure:
Typical ambient particle concentrations for PM10 (PM2.5) in Germany are in the range of 10-45 (10-30) microg/m3 as annual mean and 50-200 (40-150) microg/m3 as maximum daily mean. The ratio of PM2.5/PM10 generally amounts between 0.7 and 0.9.
Health effects:
During the past 10 years many new epidemiological and toxicological studies on health effects of particulate matter (PM) have been published. In summary, long-term exposure against PM for years or decades is associated with elevated total, cardiovascular, and infant mortality. With respect to morbidity, respiratory symptoms, lung growth, and function of the immune system are affected. Short-term studies show consistant associations of exposure to daily concentrations of PM with mortality and morbidity on the same day or the subsequent days. Patients with asthma, COPD, pneumonia, and other respiratory diseases as well as patients with cardio-vascular diseases and diabetes are especially affected. The strongest associations are found for PM2.5 followed by PM10, with no indication of a threshold value for the health effects. The data base for ultra fine particles is too small for final conclusions. The available toxicological data support the epidemiological findings and give hints as to the mechanisms of the effects.
Conclusion:
The working group concludes that a further reduction of the limit values proposed for 2005 will substantially reduce health risks due to particulate air pollution. Because of the strong correlation of PM10 with PM2.5 at most German sites there is no specific need for limit values of PM2.5 for Germany in addition to those of PM10.
The sentiment that woodsmoke, being a natural substance, must be benign to humans is still sometimes heard. It is now well established, however, that wood-burning stoves and fireplaces as well as wildland and agricultural fires emit significant quantities of known health-damaging pollutants, including several carcinogenic compounds. Two of the principal gaseous pollutants in woodsmoke, CO and NOx, add to the atmospheric levels of these regulated gases emitted by other combustion sources. Health impacts of exposures to these gases and some of the other woodsmoke constituents (e.g., benzene) are well characterized in thousands of publications. As these gases are indistinguishable no matter where they come from, there is no urgent need to examine their particular health implications in woodsmoke. With this as the backdrop, this review approaches the issue of why woodsmoke may be a special case requiring separate health evaluation through two questions. The first question we address is whether woodsmoke should be regulated and/or managed separately, even though some of its separate constituents are already regulated in many jurisdictions. The second question we address is whether woodsmoke particles pose different levels of risk than other ambient particles of similar size. To address these two key questions, we examine several topics: the chemical and physical nature of woodsmoke; the exposures and epidemiology of smoke from wildland fires and agricultural burning, and related controlled human laboratory exposures to biomass smoke; the epidemiology of outdoor and indoor woodsmoke exposures from residential woodburning in developed countries; and the toxicology of woodsmoke, based on animal exposures and laboratory tests. In addition, a short summary of the exposures and health effects of biomass smoke in developing countries is provided as an additional line of evidence. In the concluding section, we return to the two key issues above to summarize (1) what is currently known about the health effects of inhaled woodsmoke at exposure levels experienced in developed countries, and (2) whether there exists sufficient reason to believe that woodsmoke particles are sufficiently different to warrant separate treatment from other regulated particles. In addition, we provide recommendations for additional woodsmoke research.
A venture type dilution system has been introduced. Using a cascade consisting of several identical systems dilution ratios of up to 10,000 and more can easily be achieved without a prohibitively high consumption of pressurized clean air. Measurements have shown that the dilution ratio is independent of both, the particle aerodynamic diameter and the suction flow rate. The system can be used for the dilution of highly concentrated aerosols as well, within defined limits, for the decoupling of the measuring device from the aerosol system with respect to temperature and pressure.
The impact of combustion conditions on emission factors and characteristics of log wood combustion was investigated. Two different kinds of log woods (spruce and beech) and one kind of briquette (spruce sawdust) were used to study differences in emission behavior depending upon the wood type. Beech wood was used to examine additionally the impact of different moisture contents and maloperation on emissions of fine particulate matter (PM). Therefore, wood logs with three different levels of moisture content were used. Maloperation was simulated by an overload scenario and an air deficiency scenario. Toxicity equivalent (TEQ) values were calculated for the different combustion conditions. It was found that PM mass varies only by a factor of 8 at a maximum, whereas TEQ values can vary more than a factor of 80 (regular beech wood combustion, 6 μg MJ–1; beech wood combustion in an overloaded combustion chamber, 500 μg MJ–1). In particular, wood with a higher moisture content (19%) released high amounts of intermediate products from lignin and cellulose degradation. The PM emissions in this case were the highest among the tested operation conditions, especially during the initial (cold start) inflaming (660 μg MJ–1), but were not in correspondence with the toxicity potential. The TEQ (37 μg MJ–1) in that case was much lower than during maloperation.
An investigation was performed to study the emissions of state of the art small-scale residential heating appliances. The different combustion systems were compared at optimal combustion conditions. A comprehensive characterization of released organic species of all combustion systems was performed. An approach was performed to estimate the toxicity of the emitted particulate matter by the content of polycyclic aromatic hydrocarbons (PAHs). It is based on the proposal of the German Research Foundation (DFG) that the health risk is proportionally summarized by different PAHs with different health risk potentials. This approach allows for a rough but fast comparison of different furnaces by the calculation of the toxic equivalent (TEQ) value in addition to the emission of particulate matter (PM). Best results were obtained by combusting wood as pellets in a modern pellet boiler (PM = 11–13 mg MJ–1 and TEQ = 0.12–0.75 μg MJ–1). On the opposite of the emission scale, the toxic potentials of the typical log wood stove were found to be about 2 orders of magnitude higher (PM = 67–119 mg MJ–1 and TEQ = 14–28 μg MJ–1) compared to the pellet boiler, despite optimized combustion conditions.
Residential wood combustion causes major effects on the air quality on a global scale. The ambient particulate levels are known to be responsible for severe adverse health effects that include e.g. cardio-respiratory illnesses and cancer related effects, even mortality. It is known that biomass combustion derived emissions are affected by combustion technology, fuel being used and user-related practices. There are also indications that the health related toxicological effects are influenced by these parameters. This study we evaluated toxicological effects of particulate emissions (PM1) from seven different residential wood combusting furnaces. Two appliances i.e. log wood boiler and stove represented old batch combustion technology, whereas stove and tiled stove were designated as new batch combustion as three modern automated boilers were a log wood boiler, a woodchip boiler and a pellet boiler. The PM1 samples from the furnaces were collected in an experimental setup with a Dekati® gravimetric impactor on PTFE filters with the samples being weighed and extracted from the substrates and prior to toxicological analyses. The toxicological analyses were conducted after a 24-hour exposure of the mouse RAW 264.7 macrophage cell line to four doses of emission particle samples and analysis of levels of the proinflammatory cytokine TNFα, chemokine MIP-2, cytotoxicity with three different methods (MTT, PI, cell cycle analysis) and genotoxicity with the comet assay. In the correlation analysis all the toxicological results were compared with the chemical composition of the samples. All the samples induced dose-dependent increases in the studied parameters. Combustion technology greatly affected the emissions and the concomitant toxicological responses. The modern automated boilers were usually the least potent inducers of most of the parameters while emissions from the old technology log wood boiler were the most potent. In correlation analysis, the PAH and other organic composition and inorganic ash composition affected the toxicological responses differently. In conclusion, combustion technology largely affects the particulate emissions and their toxic potential this being reflected in substantially larger responses in devices with incomplete combustion. These differences become emphasized when the large emission factors from old technology appliances are taken into account.
The aim of this study was to compare four alternatives for providing decentralized energy production in small communities in terms of their flue gas emissions and toxicological properties of the emissions. In this study, two different size classes of boilers were examined and the use of fossil fuel oils was compared against wood fuels. The lowest PM1 emission, 0.1 mg MJ−1, was observed from small-scale light fuel oil combustion. In medium-scale wood combustion, PM1 emission values from a grate fired wood combustion boiler (10 MW) without particulate filtration were the highest (264 mg MJ−1) but were substantially reduced down to 0.6 mg MJ−1 due to the usage of an electrostatic precipitator (ESP). The wood combustion particles were mainly formed of potassium salts. In light fuel oil combustion, one of the main components in the particles was sulphate whereas in heavy fuel oil combustion also significant amounts of V and Ni were emitted. Pellet combustion produced the lowest PAH emissions. Overall, oil combustion produced higher amount of PAHs than wood combustion. This was indicated also as a higher cytotoxicity of the oil combustion samples when compared to those from wood combustion in the corresponding scale of boilers. However, when calculated on an equal mass basis, the particles collected after ESP were even more cytotoxic which can be explained by the altered chemical characteristics of the emissions in the ESP. Due to the variation in the emissions and in the toxicity of the emissions, we propose that in the long term, not only the emission levels but also the toxicity of the emissions should be taken into account in the regulations of the emission limits of the combustion plants.
Residential wood combustion appliances emit large quantities of fine particles which are suspected to cause a substantial health burden worldwide. Wood combustion particles contain several potential health-damaging metals and carbon compounds such as polycyclic aromatic hydrocarbons (PAH), which may determine the toxic properties of the emitted particles. The aim of the present study was to characterize in vitro immunotoxicological and chemical properties of PM1 (Dp ≤ 1 μm) emitted from a pellet boiler and a conventional masonry heater. Mouse RAW264.7 macrophages were exposed for 24 h to different doses of the emission particles. Cytotoxicity, production of the proinflammatory cytokine TNF-α and the chemokine MIP-2, apoptosis and phases of the cell cycle as well as genotoxic activity were measured after the exposure. The type of wood combustion appliance had a significant effect on emissions and chemical composition of the particles. All the studied PM1 samples induced cytotoxic, genotoxic and inflammatory responses in a dose-dependent manner. The particles emitted from the conventional masonry heater were 3-fold more potent inducers of programmed cell death and DNA damage than those emitted from the pellet boiler. Furthermore, the particulate samples that induced extensive DNA damage contained also large amounts of PAH compounds. Instead, significant differences between the studied appliances were not detected in measurements of inflammatory mediators, although the chemical composition of the combustion particles differed considerably from each other. In conclusion, the present results show that appliances representing different combustion technology have remarkable effects on physicochemical and associated toxicological and properties of wood combustion particles. The present data indicate that the particles emitted from incomplete combustion are toxicologically more potent than those emitted from more complete combustion processes.
Fine-particle and gaseous emissions from a modem small-scale pellet boiler were studied with different air-staging settings and under different load operations. Commercial wood pellets were used in the boiler, which worked with a top-feed fuel input. Partial load operation experiments included half-load 12.5 kW and low-load 7 kW. In air-staging experiments, the amounts of primary air were decreased by 71 and 82% while simultaneously keeping constant total air/fuel ratios. This was found to result in considerably lower emissions than during normal full-load operation with factory settings. The reduction in fine-particle emissions was based on both a decrease in alkali metal emissions and emissions of unburnt carbonaceous particles. However, when the amounts of secondary air were decreased by 17 and 33%, there were higher emissions of both fine particles and gases during full-load operation, especially of emission components originating from incomplete combustion. The primary air/secondary air ratio correlated with CO, PM(1), K, EC, and SO(4) emissions. Furthermore, correlations were found between the primary air/fuel ratio and particle geometric mean diameter (GMD) and between the secondary air supply and GMD. These correlations were seen with all measured points, which indicates that they apply to all of the operational situations that were studied. The results show that there is significant potential for decreasing particle emissions from automated pellet combustion systems by optimizing combustion air staging in the furnace.
Current levels of ambient air fine particulate matter (PM(2.5)) are associated with mortality and morbidity in urban populations worldwide. In residential areas wood combustion is one of the main sources of PM(2.5) emissions, especially during wintertime. However, the adverse health effects of particulate emissions from the modern heating appliances and fuels are poorly known. In this study, health related toxicological properties of PM(1) emissions from five modern and two old technology appliances were examined. The PM(1) samples were collected by using a Dekati® Gravimetric Impactor (DGI). The collected samples were weighed and extracted with methanol for chemical and toxicological analyses. Healthy C57BL/6J mice were intratracheally exposed to a single dose of 1, 3, 10 or 15mg/kg of the particulate samples for 4, 18 or 24h. Thereafter, the lungs were lavaged and bronchoalveolar lavage fluid (BALF) was assayed for indicators of inflammation, cytotoxicity and genotoxicity. Lungs of 24h exposed mice were collected for inspection of pulmonary tissue damage. There were substantial differences in the combustion qualities of old and modern technology appliances. Modern technology appliances had the lowest PM(1) (mg/MJ) emissions, but they induced the highest inflammatory, cytotoxic and genotoxic activities. In contrast, old technology appliances had clearly the highest PM(1) (mg/MJ) emissions, but their effect in the mouse lungs were the lowest. Increased inflammatory activity was associated with ash related components of the emissions, whereas high PAH concentrations were correlating with the smallest detected responses, possibly due to their immunosuppressive effect.
The characteristics and quantities of a large number of gaseous and particulate emission components during combustion in a residential wood log stove with variations in fuel, appliance and operational conditions were determined experimentally. The measurement campaign included CO, NOx, organic gaseous carbon (OGC), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions, and inorganic composition. CO varied in the range of 1100 to 7200 mg/MJfuel, while OGC varied from 210 to 3300 mg/MJfuel. Dominating VOCs were methane, followed by ethene, acetylene, and benzene. Methane varied from 9 to 1600 mg/MJfuel. The nonmethane volatile organic compound (NMVOC) emissions were in the range of 20−2300 mg/MJfuel. The PAHtot emissions varied from 1.3 to 220 mg/MJfuel, in most cases dominated by phenantrene, fluoranthene, and pyrene. PMtot were in all cases dominated by fine particles and varied in the range 38−350 mg/MJfuel. The mass median particle diameters and the peak mobility diameters of the fine particles varied in the range 200−320 and 220−330 nm, respectively, and number concentrations in the range of 1−4 × 1013 particles/MJfuel. Air starved conditions, at high firing intensity, gave the highest emissions, especially for hydrocarbons. This type of condition is seldom considered, though it may occur occasionally. The emissions from Swedish wood stoves, comparing a Swedish field study, are covered fairly well with the applied methodology, but other field studies report considerably higher emissions especially for diluted particle sampling.
Stove performance, characteristics, and quantities of gaseous and particulate emissions were determined for two different pellet stoves, varying fuel load, pellet diameter, and chimney draft. This approach aimed at covering variations in emissions from stoves in use today. The extensive measurement campaign included CO, NOx, organic gaseous carbon, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions, and inorganic composition. At high load, most emissions were similar. For stove B, operating at high residual oxygen and solely with primary air, the emissions of PMtot and particle numbers were higher while the particles were smaller. Lowering the fuel load, the emissions of CO and hydrocarbons increased dramatically for stove A, which operated continuously also at lower fuel loads. On the other hand for stove B, which had intermittent operation at lower fuel loads, the emissions of hydrocarbons increased only slightly lowering the fuel load, while CO emissions increased sharply, due to high emissions at the end of the combustion cycle. Beside methane, dominating VOCs were ethene, acetylene, and benzene and the emissions of VOC varied in the range 1.1−42 mg/MJfuel. PAH emissions (2−340 μg/MJfuel) were generally dominated by phenanthrene, fluoranthene and pyrene. The PMtot values (15−45 mg/MJfuel) were in all cases dominated by fine particles with mass median diameters in the range 100−200 nm, peak mobility diameters of 50−85 nm, and number concentrations in the range 4 × 1013 to 3 × 1014 particles/MJfuel. During high load conditions, the particulate matter was totally dominated by inorganic particles at 15−25 mg/MJfuel consisting of potassium, sodium, sulfur, and chlorine, in the form of K2SO4, K3Na(SO4)2, and KCl. The study shows that differences in operation and modulation principles for the tested pellet stoves, relevant for appliances in use today, will affect the performance and emissions significantly, although with lower scattering in the present study compared to compiled literature data.
Although organics constitute approximately 10–70% of the total dry fine particle mass in the atmosphere, their concentrations and formation mechanisms are less well understood than those of other components such as sulfate and nitrate. This is because particulate organic matter is an aggregate of hundreds of individual compounds whose concentrations cannot be characterized by a single analytical technique; more than half of the organic carbon mass has not yet been identified as individual compounds. Moreover, the collection process itself can alter the gas–particle equilibrium of a number of condensable organics resulting in both positive and negative sampling biases. The incomplete characterization of particulate organics coupled with the complexity of the photochemical reactions that produce particulate matter from volatile organic emissions has prevented the development of a first principle simulation approach. These limitations are providing an impetus for numerous scientific studies, proving organics to be the next frontier for particle characterization and simulation. This paper reviews the current state of organic aerosol sampling, analysis, and simulation, examines the limitations of the current technology, and presents prospects for the future. The emphasis is on distilling findings from recent atmospheric, smog chamber, and theoretical studies to provide a coherent picture of what has been accomplished, especially during the last five years, and what problems are ripe for further investigation.
The influence of residential wood-combustion on local air quality was studied during two periods in 2002 and 2003/04 in a small rural town with widespread use of wood combustion for heating. During one 6-week winter period, particle levels (PM2.5) in the residential area were about 4 μg m−3 higher than at a nearby background site. This was comparable to the local traffic contribution observed at a busy street (about 70,000 vehicles per day) in the city of Copenhagen. The diurnal variation in the residential area showed increased particle levels (PM2.5) in the evening and night as expected from local heating sources. Particle size distributions showed highest volume concentrations of particles with diameters of 400–500 nm, and the diurnal variation of particle volume was similar to PM2.5. The particle measurements were supported by measurements of combustion gases in both the residential area and at a background site. Receptor modelling and source apportionment of the results confirmed that the most important sources to particles were long-range transport (both organic and inorganic compounds) and local heating (particularly organic compounds) in addition to regional traffic emissions. Local wood combustion sources affected especially the organic particle component.
The fine particle and gas emissions from the residential wood combustion (RWC) appear to be a major contributor to winter-time pollution in Europe. In this study, we characterised the effect of two different combustion conditions on particulate and gaseous emissions from a conventional masonry heater. Normal combustion (NC) is the best available operational practice for the heater, whereas smouldering combustion (SC) mimicked slow heating combustion. It was found that the operational practice in RWC can significantly influence the quantity and quality of particle and gaseous emissions into the atmosphere. In SC, the emissions of carbon monoxide were 3.5-fold, total volatile organics 14-fold and PM1 6-fold to those of NC, whereas the mass of the inorganic compounds (“fine ash”) and particle number emissions were lower from SC than from NC. According to electron microscopy analyses, the observed fine ash particles seemed to occur mainly as separate spherical or irregularly shaped particles but not as agglomerates. Ultrafine (<100 nm) fine ash particles were composed mainly of K, S and Zn, but also in a lesser extent of C, Ca, Fe, Mg, Cl, P and Na. Large agglomerates were found to contain mainly carbon and are considered to be primarily soot particles. The larger spherical and irregularly shaped particles were composed of same alkali metal compounds as ultrafine particles, but they were probably covered with heavy organic compounds. From SC, particles were composed mainly of carbon compounds and they had a more closed structure than the particles from NC, due to organic matter on the particles. In the present experiments, the ultrafine mode in the particle number distributions seemed to be determined mainly by the amount of released ash forming material in combustion, and the shifting of particle size during different combustion conditions seemed to be determined by the amount of condensed organic vapour in the flue gas.
Emissions from commercial residential boilers fired with wood logs and wood pellets, have been compared. Seven boilers, selected with respect to age, design, connection to heat storage tank, and type of biofuel, were included in the study, which also covers two oil-fired boilers in comparison. The measurements of gaseous emissions comprised carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), total organic carbons (TOC), nitrogen oxides (NOx), polycyclic aromatic hydrocarbons (PAH), and 33 volatile organic compounds (VOC). Particle emissions were characterised by mass concentration, number concentration, and the corresponding particle size distributions. In general, old-type wood boilers caused considerably higher emissions than modern wood and pellet boilers. The mass concentration of particles was 180 times larger in the worst old-type case (a water-cooled wood boiler without heat storage tank) compared to the best modern case (wood pellets). The TOC emission was shown to be correlated to the CO emission, both ranging between very low values and up to 10 000 mg/MJ, depending on design and operation. The highest emissions of unoxidised compounds occurred at the highest excess air ratio, and oxygen was not the limiting parameter for poor combustion. Instead, high excess air can be suspected to cool the combustion chamber, resulting in high CO emissions. VOC was dominated by methane. Especially from an old-type boiler the methane emissions could be high and the effect on climate change then may become larger than that of an oil boiler. However, substitution of an old-type wood boiler with a modern wood boiler attached to a storage tank or with a pellet boiler, would reduce methane emissions by 8 to 9000 times and the efficiency would increase. Most emissions could be considerably lowered by connecting the old-type wood boiler to a heat storage tank, or by charging small (in relation to the combustion chamber) batches of wood.