Heikki Lamberg

Efficiency of log wood combustion affects the toxicological and chemical properties of emission particles

Context: Particulate matter (PM) has been identified as a major environmental pollutant causing severe health problems. Large amounts of the harmful particulate matter (PM) are emitted from residential wood combustion, but the toxicological properties of wood combustion particles are poorly known. Objective: To investigate chemical and consequent toxicological characteristics of PM1 emitted from different phases of batch combustion in four heating appliances. Materials and methods: Mouse RAW264.7 macrophages and human BEAS-2B bronchial epithelial cells were exposed for 24 h to different doses (15–300 µg/mL) of wood combustion particles. After the exposure, cytotoxicity, genotoxicity, production of the inflammatory mediators (TNF-α and MIP-2) and effects on the cell cycle were assessed. Furthermore, the detected toxicological responses were compared with the chemical composition of PM1 samples including PAHs, metals and ions. Results: All the wood combustion samples exerted high cytotoxicity, but only moderate inflammatory activity. The particles emitted from the inefficient phase of batch combustion in the sauna stove (SS) induced the most extensive cytotoxic and genotoxic responses in mammalian cells. Polycyclic aromatic hydrocarbons (PAHs) and other organic compounds in PM1 samples might have contributed to these effects. Instead, water-soluble metals seemed to participate in the cytotoxic responses triggered by the particles from more efficient batch combustion in the masonry heaters. Overall, the toxicological responses were decreased when the combustion phase was more efficient. Conclusion: Efficiency of batch combustion plays a significant role in the harmfulness of PM even under incomplete wood combustion processes.

Effect of fuel zinc content on toxicological responses of particulate matter from pellet combustion in vitro.

Significant amounts of transition metals such as zinc, cadmium and copper can become enriched in the fine particle fraction during biomass combustion with Zn being one of the most abundant transition metals in wood combustion. These metals may have an important role in the toxicological properties of particulate matter (PM). Indeed, many epidemiological studies have found associations between mortality and PM Zn content. The role of Zn toxicity on combustion PM was investigated. Pellets enriched with 170, 480 and 2300 mg Zn/kg of fuel were manufactured. Emission samples were generated using a pellet boiler and the four types of PM samples; native, Zn-low, Zn-medium and Zn-high were collected with an impactor from diluted flue gas. The RAW 264.7 macrophage cell line was exposed for 24h to different doses (15, 50,150 and 300 μg ml(-1)) of the emission samples to investigate their ability to cause cytotoxicity, to generate reactive oxygen species (ROS), to altering the cell cycle and to trigger genotoxicity as well as to promote inflammation. Zn enriched pellets combusted in a pellet boiler produced emission PM containing ZnO. Even the Zn-low sample caused extensive cell cycle arrest and there was massive cell death of RAW 264.7 macrophages at the two highest PM doses. Moreover, only the Zn-enriched emission samples induced a dose dependent ROS response in the exposed cells. Inflammatory responses were at a low level but macrophage inflammatory protein 2 reached a statistically significant level after exposure of RAW 264.7 macrophages to ZnO containing emission particles. ZnO content of the samples was associated with significant toxicity in almost all measured endpoints. Thus, ZnO may be a key component producing toxicological responses in the PM emissions from efficient wood combustion. Zn as well as the other transition metals, may contribute a significant amount to the ROS responses evoked by ambient PM.

Effective Density and Morphology of Particles Emitted from Small-Scale Combustion of Various Wood Fuels

The effective density of fine particles emitted from small-scale wood combustion of various fuels were determined with a system consisting of an aerosol particle mass analyzer and a scanning mobility particle sizer (APM-SMPS). A novel sampling chamber was combined to the system to enable measurements of highly fluctuating combustion processes. In addition, mass-mobility exponents (relates mass and mobility size) were determined from the density data to describe the shape of the particles. Particle size, type of fuel, combustion phase, and combustion conditions were found to have an effect on the effective density and the particle shape. For example, steady combustion phase produced agglomerates with effective density of roughly 1 g cm(-3) for small particles, decreasing to 0.25 g cm(-3) for 400 nm particles. The effective density was higher for particles emitted from glowing embers phase (ca. 1-2 g cm(-3)), and a clear size dependency was not observed as the particles were nearly spherical in shape. This study shows that a single value cannot be used for the effective density of particles emitted from wood combustion.

Optical and Chemical Characterization of Aerosols Emitted from Coal, Heavy and Light Fuel Oil, and Small-Scale Wood Combustion

Particle emissions affect radiative forcing in the atmosphere. Therefore, it is essential to know the physical and chemical characteristics of them. This work studied the chemical, physical, and optical characteristics of particle emissions from small-scale wood combustion, coal combustion of a heating and power plant, as well as heavy and light fuel oil combustion at a district heating station. Fine particle (PM1) emissions were the highest in wood combustion with a high fraction of absorbing material. The emissions were lowest from coal combustion mostly because of efficient cleaning techniques used at the power plant. The chemical composition of aerosols from coal and oil combustion included mostly ions and trace elements with a rather low fraction of absorbing material. The single scattering albedo and aerosol forcing efficiency showed that primary particles emitted from wood combustion and some cases of oil combustion would have a clear climate warming effect even over dark earth surfaces. Instead, coal combustion particle emissions had a cooling effect. Secondary processes in the atmosphere will further change the radiative properties of these emissions but are not considered in this study.