Hygroscopic Behavior of Aerosol Particles Emitted from Biomass Fired Grate Boilers (original) (raw)
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Aerosol Science and Technology, 2004
Composition, shape factor, size, and fractal dimension of soot aerosol particles generated in a propane/O 2 flame were determined as a function of the fuel equivalence ratio (φ). Soot particles were first size-selected by a differential mobility analyzer (DMA) and then analyzed by an Aerodyne aerosol mass spectrometer (AMS). The DMA provides particles of known mobility diameter (d m ). The AMS quantitatively measures the mass spectrum of the nonrefractory components of the particles and also provides the vacuum aerodynamic diameter (d va ) corresponding to the particles of known mobility diameter. The measured d m , d va , and nonrefractory composition are used in a system of equations based on the formulation presented in the companion article to estimate the particle dynamic shape factor, total mass, and black carbon (BC) content. Fractal dimension was estimated based on the mass-mobility relationship. Two types of soot particles were observed depending on the fuel equivalence ratio. Type 1: for φ < 4 (lower propane/O 2 ), d va was nearly constant and independent of d m . The value of d va increased with increasing φ. Analysis of the governing equations showed that these particles were highly irregular (likely fractal aggregates), with a dynamic shape factor that increased with d m and φ. The fractal dimension of these particles was approximately 1.7. These particles were composed mostly of BC, with the organic carbon content increasing as φ increased. At φ = 1.85, the particles were about 90% BC, 5% PAH, and 5% aliphatic hydrocarbon (particle density = 1.80 g/cm 3 ). Type 2: for φ > 4 (high propane/O 2 ), d va was linearly proportional to d m . Analysis of the governing equations showed that these particles were nearly spherical (likely compact aggregates), with a dynamic shape factor of 1.1 (versus 1 for a sphere) and a fractal dimension of 2.95 (3 for a sphere). These particles were composed of about 50% PAH, 45% BC, and 5% aliphatic hydrocarbons (particle density = 1.50 g/cm 3 ). These results help interpret some measurements obtained in recent field studies.
Determination of the fractal dimension of aerosols from kinetic coagulation
Journal of Physics D: Applied Physics, 1994
The fractal dimension of aerosol aggregates has been determined from measurements of the settling velocity of two coagulating particles and the resultant particle. The fractal dimensions for carbonaceous and magnesium oxide smoke aggregates were found to be 1.97 0.07 and 1.19 7 0.02 respectively. The measured values agree with those determined from other in situ methods, and are explainable by existing aggregation models.
International Journal of Mass Spectrometry, 2006
Various types of combustion-related particles in the size range between 100 and 850 nm were analyzed with an aerosol mass spectrometer and a differential mobility analyzer. The measurements were performed with particles originating from biomass burning, diesel engine exhaust, laboratory combustion of diesel fuel and gasoline, as well as from spark soot generation. Physical and morphological parameters like fractal dimension, effective density, bulk density and dynamic shape factor were derived or at least approximated from the measurements of electrical mobility diameter and vacuum aerodynamic diameter. The relative intensities of the mass peaks in the mass spectra obtained from particles generated by a commercial diesel passenger car, by diesel combustion in a laboratory burner, and by evaporating and re-condensing lubrication oil were found to be very similar. The mass spectra from biomass burning particles show signatures identified as organic compounds like levoglucosan but also others which are yet unidentified. The aerodynamic behavior yielded a fractal dimension (D f ) of 2.09 ± 0.06 for biomass burning particles from the combustion of dry beech sticks, but showed values around three, and hence more compact particle morphologies, for particles from combustion of more natural oak. Scanning electron microscope images confirmed the finding that the beech combustion particles were fractal-like aggregates, while the oak combustion particles displayed a much more compact shape. For particles from laboratory combusted diesel fuel, a D f value of 2.35 was found, for spark soot particles, D f ≈ 2.10. The aerodynamic properties of fractal-like particles from dry beech wood combustion indicate an aerodynamic shape factor χ that increases with electrical mobility diameter, and a bulk density of 1.92 g cm −3 . An upper limit of χ ≈ 1.2 was inferred for the shape factor of the more compact particles from oak combustion.
Comparison of three methods of fractal analysis applied to soot aggregates from wood combustion
Journal of Aerosol Science, 2006
The morphological and dynamic properties of fractal-like particles produced from the combustion of wood are studied in this work. Particles with electrical mobility diameters of 200, 275, 350 and 450 nm were deposited on filters and imaged using a high-resolution scanning electron microscope (SEM). The soot particles consisted of aggregated primary spheres with mean radius a p = 25.5 ± 3.5 nm and standard deviation g = 1.27 ± 0.09. The fractal dimension of the aggregates, D f , was derived from three techniques: (1) D f = 1.84 ± 0.05 from the projected surfaces in the SEM images;
Journal of Aerosol Science, 1994
Abslraet--A method is presented, using a modified Millikan cell, to measure the fractal dimension (D) of in situ carbonaceous agglomerates in three dimensional space, From the measured aerodynamic diameter (sedimentation technique) and the mass of the agglomerate (photoelectric technique), D of an individual agglomerate is derived. Results, in the range of 1.87 ~<D ~<2.19, were in good agreement with those of several theories and calibration against polyvinyltoluene spheres which gave 2.96 ~< D ~< 2.99.
Particle size distributions of ultrafine combustion aerosols generated from household fuels
Atmospheric Pollution Research, 2014
In the present study, the number size distributions of aerosols generated from five commonly and widely used household fuels namely firewood, coal, dung cake, kerosene stove and LPG stove were investigated using scanning mobility particle sizer (SMPS). Important parameters of PSD such as total number concentration, geometric mean (GM) and geometric standard deviation (GSD) for tested fuels were evaluated and compared. It was found that solid biomass (firewood and dung cake) generates higher particle number concentrations then non-solid fuels i.e. kerosene and LPG stove. For all biomass fuels the number concentrations were in the order of 10 7 particle/cm 3. The geometric mean diameter was highest for dung cake generated aerosols, while LPG and coal generated aerosol showed lower GM diameter. The geometric mean diameter varied between 48 nm and 152 nm for all tested fuels. The geometric standard deviation values of all tested fuels revealed that in solid biomass combustion, there was more dispersion in aerosol sizes than non-solid fuels. The number concentration emitted by LPG was found to be the lowest among all fuels and the GSD was also the lowest.
Impact of combustion conditions on physical and morphological properties of biomass burning aerosol
Aerosol Science and Technology
The study of biomass burning particle density provides information on aging, new particle formation, transport properties, and is an important parameter in aerosol impacts modeling. Density is used in mass closure techniques to estimate the temporal resolution of particulate mass concentrations. However, the study of BB particle density as a function of burning conditions is still limited. Laboratory measurement of six sub-Saharan African biomass fuels burned under a range of conditions, from pure smoldering to pure flaming conditions, is presented. Smoldering-dominated burning (modified combustion efficiency (MCE) < 0.9) particles has a very narrow range of effective density (q eff) 1.03 g cm À3 to 1.21 g cm À3 and a mass mobility exponent (D fm) of $3 (2.97 ± 0.05), indicating that they are spherical particles. For the flaming-dominated burning (MCE >0.95) particles, show a size dependent q eff for all six different fuels. In this case, the mean and standard deviation of the q eff decreased with increasing size, from (0.94 ± 0.21) g cm À3 at a mobility diameter of 80 nm to (0.31 ± 0.07) g cm À3 at a mobility diameter of 400 nm. The size-dependent q eff of flamingdominated aerosol suggests the fractal nature of freshly emitted particles. The relationship between D fm and the MCE shows three distinct morphology regimes, which we define as the spherical particle, the transition, and the fractal regime. Our proposed relationship of D fm with the MCE can be used as a tool to assess the applicability of Mie theory for optical closure calculations in the absence of particle morphological information.
Environmental Science & Technology, 2014
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.