Validation of a novel Real-LIFE test protocol on two log wood stoves

Abstract. Wood combustion emissions can induce oxidative stress in the human respiratory tract by reactive oxygen species (ROS) in the aerosol particles, which are emitted either directly or formed through oxidation in the atmosphere. To improve our understanding of the particle-bound ROS (PB-ROS) generation potential of wood combustion emissions, a suite of smog chamber (SC) and potential aerosol mass (PAM) chamber experiments were conducted under well-determined conditions for different combustion devices and technologies, different fuel types, operation methods, combustion regimes, combustion phases, and aging conditions. The PB-ROS content and the chemical properties of the aerosols were quantified by a novel ROS analyzer using the DCFH (2′,7′-dichlorofluorescin) assay and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). For all eight combustion devices tested, primary PB-ROS concentrations substantially increased upon aging. The level of primary and aged PB-ROS emission factors (EFROS) were dominated by the combustion device (within different combustion technologies) and to a greater extent by the combustion regimes: the variability within one device was much higher than the variability of EFROS from different devices. Aged EFROS under bad combustion conditions were ∼ 2–80 times higher than under optimum combustion conditions. EFROS from automatically operated combustion devices were on average 1 order of magnitude lower than those from manually operated devices, which indicates that automatic combustion devices operated at optimum conditions to achieve near-complete combustion should be employed to minimize PB-ROS emissions. The use of an electrostatic precipitator decreased the primary and aged ROS emissions by a factor of ∼ 1.5 which is however still within the burn-to-burn variability. The parameters controlling the PB-ROS formation in secondary organic aerosol were investigated by employing a regression model, including the fractions of the mass-to-charge ratios m∕z 44 and 43 in secondary organic aerosol (SOA; f44−SOA and f43−SOA), the OH exposure, and the total organic aerosol mass. The regression model results of the SC and PAM chamber aging experiments indicate that the PB-ROS content in SOA seems to increase with the SOA oxidation state, which initially increases with OH exposure and decreases with the additional partitioning of semi-volatile components with lower PB-ROS content at higher OA concentrations, while further aging seems to result in a decay of PB-ROS. The results and the special data analysis methods deployed in this study could provide a model for PB-ROS analysis of further wood or other combustion studies investigating different combustion conditions and aging methods.

This study reports the potential toxicological impact of particles produced during biomass combustion by an automatic pellet boiler and a traditional logwood stove under various combustion conditions using a novel profluorescent nitroxide probe, BPEAnit. This probe is weakly fluorescent but yields strong fluorescence emission upon radical trapping or redox activity. Samples were collected by bubbling aerosol through an impinger containing BPEAnit solution, followed by fluorescence measurement. The fluorescence of BPEAnit was measured for particles produced during various combustion phases: at the beginning of burning (cold start), stable combustion after refilling with the fuel (warm start), and poor burning conditions. For particles produced by the logwood stove under cold-start conditions, significantly higher amounts of reactive species per unit of particulate mass were observed compared to emissions produced during a warm start. In addition, sampling of logwood burning emissions after passing through a thermodenuder at 250 degrees C resulted in an 80-100% reduction of the fluorescence signal of the BPEAnit probe, indicating that the majority of reactive species were semivolatile. Moreover, the amount of reactive species showed a strong correlation with the amount of particulate organic material. This indicates the importance of semivolatile organics in particle-related toxicity. Particle emissions from the pellet boiler, although of similar mass concentration, were not observed to lead to an increase in fluorescence signal during any of the combustion phases.

• Suitable combustion behavior was observed, although NOx and PM emissions exceeded the standard limit. • Homogeneous nucleation of alkali vapors is the main PM formation mechanism at nominal load. • Heterogeneous condensation of alkali chlorides and sulphates is the dominated PM formation mechanism al partial load. • Low deposition rate and no problems related to fouling are expected. This work evaluates the suitability of bagasse from grape seed oil extraction as a fuel for domestic boilers. Results showed an acceptable combustion efficiency (higher than 90 %) at both partial (24 kW) and nominal (55 kW) load. CO emissions (150 and 1200 mg/Nm 3 at nominal and partial load, respectively) fulfill the UN-EN 303-5 for class 3 boilers. However, although PM emissions were lower than expected (due to the high ash content of the residue, ∼4 % d.b), only PM at partial load fulfill the cited standard. In general, PM agglomerates with different sizes (depending on the load) but comparable shape and composition (mainly K, S, Cl and Na) were observed. The effect of the load was not significant for the smallest particles (PM 0.1 ), homogeneous nucleation of alkali vapors appearing as the main formation mechanism at both conditions. However, while bigger particles were formed through heterogeneous condensation of alkali chlorides and sulphates followed by agglomeration and coalescence at partial load, unburnt fuel together with fly ash dominated at nominal load. Finally, condensation of alkaline salts in the flue gas and their transport to the heat exchanger surface by diffusion or thermophoresis has been elucidated as the main route leading to fouling.

Adverse health effects of condensable organic compounds (COC) and potential secondary organic aerosols from wood combustion emissions are difficult to determine. Hence, available information is usually limited to a small number of specific applications. Therefore, we introduced a simple, fast, and economic method where water-soluble COC (WSCOC) and WSCOC together with water-soluble primary solid particles (WSpSP) from wood combustion were sampled and subsequently exposed to cultured human lung cells. Comparing the cell viability of H187 human epithelial lung cells from five combustion devices, operated at different combustion conditions, no, or only a minor, cytotoxicity of WSCOC is found for stationary conditions in a grate boiler, a log wood boiler, and a pellet boiler. All combustion conditions in a log wood stove and unfavorable conditions in the other devices induce, however, significant cytotoxicity (median lethal concentration LC50 5-17 mg/L). Furthermore, a significant correlation between CO and cytotoxicity was found ( R2 ∼ 0.8) suggesting that the simply measurable gas phase compound CO can be used as a first indicator for the potential harmfulness of wood combustion emissions. Samples containing WSCOC plus WSpSP show no additional cytotoxicity compared to samples with COC only, indicating that WSCOC exhibit much higher cytotoxicity than WSpSP.

The biomass market has experienced an increase in development, leading to research and development efforts that are focused on determining optimal biofuel combustion conditions. Biomass combustion is a complex process that involves divergent parameters and thus requires the use of advanced analysis methods. This study proposes combining grey relational analysis (GRA) and error propagation theory (EPT) to select a biofuel and its optimal combustion conditions. This research will study three biofuels that are currently used in a region of South Europe (Spain), and the most important variables that affect combustion are the ignition front propagation speed and the highest temperature that is reached at the fixed bed combustor. The results demonstrate that a combination of both theories for the analysis of solid-state thermochemical phenomena enables a fast and simple way of choosing the best configuration for each fuel.

A laboratory based comparative study of Indian biomass cookstove testing protocol and Water Boiling Test

The effects of operating conditions on emissions from masonry heaters and sauna stoves

Assessment of clean cooking technologies under different fuel use conditions in rural areas of Northern India

The presented wood combustion emission study employing a logwood stove showed that four burning phases of different aerosol compositions and different amounts of emitted particulate matter (PM) occurred during a combustion batch. As a novel approach, in this study, the burning phases were defined by chemical changes in the aerosol gas phase during combustion, instead of being linked to predefined time periods or the amount of PM emissions. This deeper view into the aerosol chemistry of the different burning phases was possible by employing online mass spectrometry techniques with high time resolution. A special soft ionization technique enabled the selective detection of polyaromatic hydrocarbons (PAHs) in the gas phase, whereas changes in the particle phase were observed by aerosol mass spectrometer (AMS). The use of AMS allowed the description of changes in the particle phase and in the amounts of PM emitted during the burning phases, as well as verification of the observed burning phases. Finally, it was shown that the organic fraction and the amount of particles emitted during the ignition phase were main contributors to the emitted PM. The definition of these four burning phases was supported by a more detailed investigation of the chemistry of the organic matter using a Van Krevelen description (average H/C ratios of 1.32–1.64 and O/C ratios of 0.25–0.44, with individual values up to 1.4) along with our novel approach of employing positive matrix factorization (PMF) as a source apportionment tool for the separation of one emission source into different combustion-dominated processes. In addition, the highly dynamic and complex nature of wood combustion emissions was revealed by these analysis methods. It was shown that different combustion conditions have a strong impact on the amount of emitted PM. For instance, an experiment with an overloaded stove emitted a roughly 4-fold higher mass of PM compared to a stove run under the manufacturer’s recommended (normal) combustion conditions. This experiment showed a much higher amount of PAHs, which are very harmful for human health.

The 2018 Wood Stove Design Challenge was an international design competition which sought to identify top performing residential wood stoves based on automation. To prepare for the event, the Northeast States for Coordinated Air Use Management (NESCAUM) developed a testing protocol that challenged the stoves by testing them in more field-like conditions—capturing emissions from start-up, reloading a stove, and the use of larger piece sizes. Flue gas emissions were measured using a combination of in-stack and novel dilution sampling methods, as the event occurred on the National Mall in Washington D.C. in a non-laboratory setting. Particulate matter (PM), carbon monoxide (CO), carbon dioxide (CO2), and methane (CH4) were measured from three stoves in real-time. A combustion efficiency was also calculated for each stove in real-time. Measured PM emission rates ranged between 1.8 and 8.0 g/hr for all stoves and operating conditions, with the highest emissions being measured during cold start in all cases. The test average PM emission rates were 2.4, 4.0, and 2.4 g/hr for stoves A, B, and C, respectively. Results showed emissions measured during transient operations, which are often excluded in current certification methods, can be significantly higher than steady-state periods—echoing other studies and highlighting the importance of testing in various operational modes for more realistic emission estimates. Additionally, the stoves had overall CO emission rates of 48.8, 284.8, and 100.8 g/hr, for stoves A, B and C, respectively. Calculated PM and CO emission factors overall were low considering the testing protocol sought to follow more challenging yet realistic practices in terms of fuel loading and operating procedures. The overall estimated combustion efficiency for stoves A, B, and C was 85%, 78%, 76%, respectively and in all cases was lowest during the cold start period.This report details the successfully proposed and assembled instrumentation that was relatively portable for field-site testing and the results of the emissions measurements for the 2018 Wood Stove Design Challenge competition. Overall, the repeatability of each stove was favorable with coefficients of variation (COV) ranging from 7 to 15% for measured PM concentrations.

Smoke from residential wood burning has been identified as a major contributor to air pollution, motivating detailed emission measurements under controlled conditions. A series of experiments were performed to compare the emission levels from two types of wood-stoves to those of fireplaces. Eight types of biomass were burned in the laboratory: wood from seven species of trees grown in the Portuguese forest (Pinus pinaster, Eucalyptus globulus, Quercus suber, Acacia longifolia, Quercus faginea, Olea europaea and Quercus ilex rotundifolia) and briquettes produced from forest biomass waste. Average emission factors were in the ranges 27.5-99.2 g CO kg(-1), 552-1660 g CO(2) kg(-1), 0.66-1.34 g NO kg(-1), and 0.82-4.94 g hydrocarbons kg(-1) of biomass burned (dry basis). Average particle emission factors varied between 1.12 and 20.06 g kg(-1) biomass burned (dry basis), with higher burn rates producing significantly less particle mass per kg wood burned than the low burn rates. Particle mass emission factors from wood-stoves were lower than those from the fireplace. The average emission factors for organic and elemental carbon were in the intervals 0.24-10.1 and 0.18-0.68 g kg(-1) biomass burned (dry basis), respectively. The elemental carbon content of particles emitted from the energy-efficient "chimney type" logwood stove was substantially higher than in the conventional cast iron stove and fireplace, whereas the opposite was observed for the organic carbon fraction. Pinus pinaster, the only softwood species among all, was the biofuel with the lowest emissions of particles, CO, NO and hydrocarbons.

In 2018, the International Organization for Standardization (ISO) 19867-1 "Harmonized laboratory test protocols" were released for establishing improved quality and comparability for data on cookstove air pollutant emissions, efficiency, safety, and durability. This is the first study that compares emissions [carbon dioxide, carbon monoxide, total hydrocarbons, methane, nitrogen oxides, fine particulate matter (PM2.5), organic carbon, elemental carbon, and ultrafine particles] and efficiency data between the ISO protocol and the Water Boiling Test (WBT). The study examines six stove/fuel combinations [liquefied petroleum gas (LPG), pellet, wood fan, wood rocket, three stone fire, and charcoal] tested in the same US EPA laboratory. Evaluation of the ISO protocol shows improvements over previous test protocols and that results are relatively consistent with former WBT data in terms of tier ratings for emissions and efficiency, as defined by the ISO 19867-3 "Voluntary Performance Targets." Most stove types remain similarly ranked using ISO and WBT protocols, except charcoal and LPG are in higher PM2.5 tiers with the ISO protocol. Additionally, emissions data including polycyclic aromatic hydrocarbons are utilized to compare between the ISO and Firepower Sweep Test (FST) protocols. Compared to the FST, the ISO protocol results in generally higher PM2.5 tier ratings.

Present work reports thermal and emission performance of in-house developed natural and forced draft metal biomass cookstoves. Laboratory as well as field tests are performed on the cookstoves. Experiments are performed on natural draft metal cookstove in laboratory at different air supply hole openings. Decrease in average input power and average thermal efficiency is observed between 3.74-3.43 kW and 31.14-29.45% respectively. Variation in average emission factor for carbon monoxide (CO) is found to be between 3.5-9.9 g/MJd. Emissions of Oxides of Nitrogen (NOx) are found to be varying between 1 ppm to 13.5 ppm without any specific trend. Experiments are performed on forced draft metal cookstove in laboratory on two fan speeds. The average input power and average thermal efficiency vary between 3.4-3.0 kW and 36.9-42.5% respectively. Variation in average emission factor for CO is found to be between 1.8-4.5 g/MJd and that of average NOx emissions between 16.8-2.5 ppm.During field tests, amount of fuel consumption and emissions of CO for both the cookstoves is compared with traditional cookstoves used by two families. In case of Family A, there is a saving in fuel consumption by 19% and 40% with natural draft and forced draft metal cookstoves respectively. The corresponding values for Family B are 5 % and 24% respectively. In case of Family A, there is decrease in CO emissions by 89% and 86% with natural draft and forced draft metal cookstoves respectively. The corresponding values for Family B are 76% and 82% respectively.

Reduction of gaseous and particulate emissions from small-scale wood combustion with a catalytic combustor

Validation of a Novel Real-Life Test Protocol on Two Log Wood Stoves