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As concerns about climate change and sustainability rise, biomass utilization has a potential to become one of the pillars of the future energy market. It is therefore critical to assure that solid biomass fuels are of the highest quality and do not contribute to avoidable air pollution. Our research has shown that petrographic analysis of solid biomass in reflected light can quickly and reliably provide information on fuel composition and contamination. As such, this technique has a potential to improve our understanding of raw fuel properties and, in some instances, even predict parameters of their combustion emissions. This paper provides guidelines for conducting microscopic analysis of wood pellets and charcoal-based fuels in reflected light. It presents two preliminary microscopic classifications of solid biomass components and emphasizes the need for training materials, exemplified by recently published photomicrograph atlases. Our research indicates that pairing reflected light microscopy with the currently used standard testing would enhance the quality assessment of solid biomass. To achieve this, the methodology must be promoted, tested for interlaboratory reproducibility, and finally standardized. • Solid biomass products contain a wide range of contaminations. • Reflected light microscopy is effective tool to study impurities in solid biomass. • Petrographic analysis can complement and enhance currently used quality testing. • Methodology requires further development, refining and ultimately standardization. [ABSTRACT FROM AUTHOR]

Considering global market trends and concerns about climate change and sustainability, increased biomass use for energy is expected to continue. As more diverse materials are being utilized to manufacture solid biomass fuels, it is critical to implement quality assessment methods to analyze these fuels thoroughly. One such method is reflected light microscopy (RLM), which has the potential to complement and enhance current standard testing, leading to improving fuel quality assessment and, ultimately, preventing avoidable air pollution. An interlaboratory study (ILS) was conducted to test the reproducibility of biomass fuels component identification using a reflected light microscopy technique. The exercise was conducted on thirty photomicrographs showing biomass and various undesired components (like plastics or mineral matter), which were purposely added (by the ILS organizers) to contaminate wood pellets and charcoal-based grilling fuels. Forty-six participants had various levels of difficulty identifying the marked components, and as a result, the percentage of correct answers ranged from 52.2 to 94.4%. Among the most difficult components to distinguish were petroleum products and inorganic matter. Various reasons led to the misidentification, including insufficient morphological descriptions of the components provided to participants, ambiguities of the nomenclature, limitations of the analytical and exercise method, and insufficient experience of the participants. Overall, the results indicate that RLM has the potential to enhance the quality assessment of biomass fuels. However, they also demonstrate that the petrographic classification used in this exercise requires further refinement before it can be standardized. While a new simplified classification of solid biomass fuels components was created as an outcome of this study, future research is necessary to refine the nomenclature, develop a microscopic morphological description of the components, and verify the accuracy of component identification with a follow-up ILS. • Study documents utility of reflected light microscopy in studying biomass fuels. • RLM has significant potential in the quality assessment of solid biomass fuels. • A new classification of solid biomass microscopic components is proposed. • Developing a microscopic morphological description of the components is needed. [ABSTRACT FROM AUTHOR]

With interest rising in biomass use, biomass gasification has the potential to become an imperative mechanism to deliver clean conversion of various types of solid biomass to gas. But as biomass gasification attracts growing interest, it is important to focus not only on the technological feasibility but also fully understand its environmental impact to eliminate avoidable air pollution. In this study, we investigated relationships between the composition of 14 types of solid biomass fuels and their gasification emissions in a small-scale residential outdoor setting. Our results show that the amount and type of produced emissions are strongly influenced by the gasified feed. Combining chemical and petrographic analysis proved to be a robust quality assessment method of solid biomass fuels, allowing for quick detection of their contaminants. These impurities can be directly correlated with elevated particulate matter emissions, CO, H 2 S, HCHO, NH 3 , SO 2 , NO x , and respiratory tract irritants. These observations show that quality testing of biomass fuels is critical not only for ensuring their high quality but also for predicting avoidable air pollution during their utilization. Although our data revealed relationships between the type of biomass fuel and gasification emissions, in general, our experiments show that small-scale gasification in a residential setting is a safe technology, and potential hazards can be eliminated by using certified fuels and ensuring appropriate distance from the source of emissions. • Biomass gasification can deliver clean conversion of solid biomass to gas. • Gasification emissions depend on the type of biomass fuel. • Solid biomass products contain a wide range of contaminations. • Results of petrographic analysis can be correlated with emissions. [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted to assess air pollution and human health risks arising from exposure to outdoor cooking, but limited standards have been implemented around the world to assure fuel quality. While charcoal briquettes and lumps are a popular fuel choice for grilling, almost no data specifying their properties are available to consumers. Because the properties of fuels affect the flue gases, it is critical to understand how the quality of grilling briquettes and lumps translates not only into the quality of the grilled food, but, even more importantly, how their emissions impact human safety and the environment. The main purpose of this study is to investigate the impacts of the quality of charcoal briquettes and lumps on potentially harmful emissions during grilling. To analyze their quality, we used reflected light microscopy to identify a range of contaminants, including biomass, mineral matter, coal, coke, metal, rust, plastics, glues, and synthetic resins, in 74 commercially available products made in Poland, the United States of America, Ukraine, Germany, Belarus, the Czech Republic, and the Republic of South Africa. Our data show that majority of the products analyzed do not meet the existing quality standard EN 1860-2:2005 (E) of less than 1% contaminants, some of these products contain up to 26.6% of impurities. The amount of contaminants correlates with particulate matter, as well as CO and CO 2. The contribution of biomass is especially significant because it can be used to predict harmful particulate matter emissions during grilling. The relationship between the composition of charcoal briquettes and lump charcoal and their emissions is particularly strong during the first 15 to 20 min after ignition (when emissions are the highest), therefore, this initial stage is especially unsafe to consumers, and staying away from the grill during this time is recommended. Unlabelled Image • Reflected light microscopy can be valuable tool to study impurities in pellet fuels. • Some lump charcoal and charcoal briquettes contain a wide range of impurities. • Detected contaminants were biomass, coal, coke, metals, sand, plastic, and glass. • Contamination often exceeded 1% by volume that has been established in standards. • There are relationships between impurities and the emissions during grilling. [ABSTRACT FROM AUTHOR]

As the interest in the renewable resources has been increasing worldwide, the wood pellet sector has the potential to become a mainstream fuel of the future in the heat market. This development is especially noted in the European Union countries which consumed 50 % of global wood pellets in 2018. While only about 2 % of the United States energy consumption was derived from wood and wood waste in 2018, the U.S. pellet production continues to grow exponentially due to high demand from overseas markets. The U.S. pellet production was 8.2 million tons in 2018, making the United States the second largest producer of pellets in the world, surpassed only by China. In this growing market, a question has emerged: How can pellet quality be reliably assured? Current standards test the quality of pellets based on a variety of physical and chemical properties. However, some impurities in pellets (glass, plastic, metal, ceramics, coal, and coke) cannot be identified this way. Those impurities can have negative impacts on the environment, human health, and the durability of stoves. A quick and simple way to identify and quantify impurities in pellet fuels such as wood pellets and grilling briquettes is by using petrographic methods. In this study we used reflected light microscopy to identify a range of contaminants including bark, glass, plastic, coal, coke, slag, mineral matter, and metals in 514 commercially available wood pellets made in Poland, Ukraine, Germany, and the United States. Our results demonstrate that optical microscopy could become an effective tool for assessing the purity of wood pellets, and as such, it might be a valuable addition to physical and chemical tests used in the current standards. • Reflected light microscopy can be an effective tool to study impurities in pellet fuels. • Some pellets contain a wide range of impurities, often exceeding the 2 %-weight that has been established in standards. • The most commonly detected contaminants included bark, coal, coke, metals, sand, plastic, and glass. • The classification of contaminants in this study is preliminary and may need to be refined when more data became available. [ABSTRACT FROM AUTHOR]