10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
High-temperature DMA Analysis of Wood Combustion Originated Particles
Heikki Lamberg, OLLI SIPPULA, Jorma Joutsensaari, Mika Ihalainen, Jarkko Tissari, Anna Lähde, Jorma Jokiniemi, University of Eastern Finland
Abstract Number: 784 Working Group: Carbonaceous Aerosol
Abstract Soot particles from combustion sources are known to have significant environmental effects. One of the major sources of soot particles is small-scale wood combustion, and there is an urgent need to develop methods to abate soot emissions from these appliances. The oxidation of soot particles in the combustion chamber is essential for the control of harmful emissions. Thus, the oxidation characteristics of wood combustion particles were studied in a high-temperature tandem differential mobility analyzer, which contained particle classification, a high-temperature reactor and scanning mobility particle sizer for measuring any possible changes in particle size taking place inside the reactor.
Particles were generated using a pellet boiler, which was operated with low load mode to increase the proportion of soot within the particles, and a wood stove. The aerosol was diluted using a porous tube diluter and an ejector diluter, and led to a sampling chamber that stabilized the small variation in the particle concentration generated by the combustion process. Sample was led from the chamber to a differential mobility analyser, which classified particles to a certain size class (40 nm, 100 nm or 200 nm). This was followed by a temperature-controlled laminar flow reactor. The oxygen concentration in the reactor was close to atmospheric concentration because of the sample dilution. Temperature inside the reactor tube was varied up to 1000 °C and the changes in the particle size were measured using a scanning electrical mobility analyser (SMPS, TSI Inc.). Particle samples were additionally collected for chemical analysis and electron-microscope analysis and transmission electron microscopy. Finally, kinetic parameters for assessing wood combustion soot oxidation under conditions representing the post-combustion zone of small appliances were derived.
Chemical analyses of the PM1 samples showed that about 50% of the PM1 was composed of EC and about 10% of OC. The most abundant inorganic species were potassium, sodium, sulphate, chloride and nitrate. Their total share was about 25% of the total PM1.
There was no considerable oxidation of the wood combustion particles below 400 °C. In all particle sizes in pellet combustion, the minimum particle sizes were reached at 750 °C, while wood stove particles were not fully oxidized at 900 °C. At 750 °C, both 100 nm and 200 nm pellet combustion particles reached GMD 28 nm, and 40 nm particles reached GMD 19 nm. At 900 °C there was no particle mode left; soot particles in 100 nm size were oxidized at 750 °C and once temperatures reached 900 °C, also inorganic particles were evaporated. Furthermore, the double mode in 600 °C indicated that there were two types of particles in the 100 nm size, for which the oxidation rate was different.
This difference is a result of the high alkali metal content in pellet combustion particles, which presumably leads to catalytically enhanced oxidation of soot particles. However, the wood stove particles with low alkali metal content also had lower oxidation temperatures compared to previously studied diesel combustion particles. According to the fitting parameters, about 70% particle reduction could be achieved with one second residence time at 800 °C. These results can be utilized in the development of strategies and technologies to abate soot emissions from small-scale wood-fired combustion appliances.