Study on soot and other refractory components from various combustion processes

Combustion processes emit remarkable amount of particles into the atmosphere. These particles are released e.g. from the spark ignition and diesel engines of road-traffic and from the combustion processes of small and large-scale energy production. Burning technologies and conditions as well as fuels combusted influence strongly on physical and chemical characteristics of particle emissions. It is important to know the properties of these emissions and causes behind them to analyze their impact on global radiative balance as well as on local and regional air quality and human health. The objective of this thesis was to improve knowledge of chemical and physical properties of particles emitted from different combustion processes using modern measurement and data handling techniques. The thesis mostly concentrated on refractory part of the particles that is, the part that is highly heat resistant (i.e. black carbon (BC), low-volatile organics, inorganic minerals). One part of the thesis tested a method that enabled the determination of non-volatile (or refractory) fraction of particles from the ambient air that was supposed to be soot emitted from traffic. The results were compared with other measurement and modelling results leading to possibility to estimate the mixing state and refractive indices of particles. The results showed that the method reliable gave information about soot fraction, mixing state and refractive indices of ambient air particles. It was possible to estimate when air masses were influenced by particles freshly emitted from traffic. In addition to method testing, the thesis concentrated on studies of primary particle emissions from residential wood and wood pellet combustion as well as from large-scale combustion of heavy fuel oil (HFO) and coal. The emissions were characterized based on versatile instrumentation and data handling techniques leading to the information about chemical composition, size distribution, optical, radiative forcing and hygroscopic properties of particles emitted from investigated combustion cases. Overall, particle emissions of large-scale combustion of oil and coal were clearly lower than those of small-scale wood fuel combustion. However, differences inside largeand small-scale combustion were also significant depending on combustion and cleaning technique, fuel and combustion conditions. Especially particles emitted from masonry heater included remarkable fractions of particulate organic matter and BC whereas large-scale hardly emitted any. High BC fraction led to low single scattering albedo and thus, to positive radiative forcing effect over a dark surface. Surprisingly, also some cases of HFO combustion led to particle emissions with positive radiative forcing effect. Particle emissions of HFO combustion were also hygroscopic indicating that these particles could have significant effect on cloud formation in the atmosphere. In coal combustion, effective cleaning technique diminished the uncleaned emissions, which also were rather low, to a fraction from the original emissions. To conclude, versatile measurement and analyze techniques used in the investigations of this thesis enabled accurate characterization of particles emitted from different combustion sources. The results clearly showed that the knowledge of the cause and effects relationship between combustion process and particle properties is crucial in assessment of climatic and health effects of particles and on the other hand, in finding the combustion techniques that minimize emissions. Publishing unit Finnish Meteorological Institute, Atmospheric Composition Research Classification (UDC)