Recently, as a soot formation model, the method of moments (MOM) for soot particle size distribution function (PSDF) is used in many studies. In this method, soot number and mass densities transport equations are solved to predict the soot formation behavior. In addition, the soot formation is regarded as the combination of major four processes such as nucleation, coagulation, surface growth and oxidation, and the concentrations of soot precursors needed in the nucleation are predicted using the detailed or reduced mechanisms of chemical reactions. In this paper, the soot formation models are reviewed and an example of the numerical simulation of soot formation in a combustion field is introduced. The soot formation in a spray flame is targeted here. The results show that the soot is formed in the spray diffusion flame region and its radiation emission increases with the equivalence ratio of the droplet fuel. This trend is in good agreement with that of the luminous flame behavior observed in the experiment. The radiation is found to strongly affect the soot formation behavior. Without the radiation model, the soot volume fraction is fatally overpredicted.
The photooxidation of aromatic hydrocarbons (AHCs) is one of the potential sources of secondary organic aerosol (SOA) in urban air, but the explicit reaction mechanisms of these SOA formations have not been elucidated. In this study, we measured SOA yields during oxidation of four AHCs from a series of laboratory experiments. The SOA yields from toluene, p-ethyltoluene, p-xylene and 1,3,5-trimethylbenzene were 0.07-0.11, 0.06-0.10, 0.02-0.04 and 0.02-0.03, respectively; the SOA yield from each AHC depended on the initial AHC concentration. On the basis of a previous reaction mechanism, in which condensable products are assumed to be formed by secondary reactions of primary oxidation products with ozone, the SOA concentrations were calculated and compared with the experimental results. As for each AHC, SOA yields measured at different initial AHC concentrations could be explained by assuming that the overall yield of primary oxidation products which forms SOA is constant being independent of the initial AHC concetration.
A new electrosplay pyrolysis method where droplets are broken by a rectangular ac high voltage (named rectangular ac electrosplay pyrolysis method) is developed. The new method is compared with electrosplay pyrolysis methods using dc high voltage and using ac high voltage. X-ray diffraction patterns showed that particles synthesized from zinc nitrate and thiourea/distilled water solution and their/ethyl alcohol solution with the new method were ZnS. Deposition ratios and collection yield of the rectangular method were higher than the dc method but worse than the ac method. The mean diameters of particles formed by the rectangular method are respectively 194 nm and 41 nm when distilled water and ethanol were used as the solvent. These values were close to the mean diameter of particles formed by the dc method but much smaller than those by the ac method.
We have measured the effects of discharge polarity on the formation of fine particles from SO2 by DC corona discharges in order to study the role of gaseous ions in the desulfurization process of flue gases by using discharge plasmas. For both positive and negative discharges, the number concentration of the formed particles in SO2/H2O/Air mixtures increased with SO2 (0-1 ppm) and H2O (5 × 102-3 × 103 ppm) concentrations. However, the positive discharges produced a larger amount of particles, and the size of which was larger than those formed by negative discharges. The fraction of charged particles dropped significantly with increasing the number concentration of formed particles in the case of positive discharges, while large fractions of charged particles were observed for negative discharges under all conditions. Mass spectrometric measurements confirmed the formation of H2SO4 by negative discharges through the detection of HSO4- ions in the negative ion mass spectra . On the other hand, no positive ions of H2SO4 were found in the mass spectra of positive ions formed by positive discharges. However, the dominance of H3O+ ions in the spectra suggested that the formation of OH radicals and the subsequent formation of H2SO4 took place also in the case of positive discharges. Because of its high electron affinity, H2SO4 formed by negative discharges is easily ionized to HSO4- ions by the reactions with the surrounding negative ions, which leads to the charged particle formation via ion-induced nucleation. On the contrary, since H2SO4 hardly reacts with positive ions and remains neutral with positive ions, the most of particles are formed via homogenous nucleation by positive discharges.
We evaluate the size distribution of fine water droplets produced by electrostatic atomization using a differential mobility analyzer (DMA) and a condensation nucleus counter (CNC) . Broad size distribution with the peak of mobility diameter of around 15-20 nm is observed for the neutralized polydisperse water droplets. The number of charge is analyzed using a tandem DMA system. The water droplets are highly charged depending on the particle size. The number of maximum electric charges is 14, which is well below the Rayleigh limit.
In order to analyze the urban atmospheric particles in Asia, we have undertaken simultaneous measurements of aerosols and suspended particulate matter (SPM) at a NASA/AERONET station at Kinki University Campus, Higashi-Osaka, since March in 2004. The relationship between concentration of suspended particulate matter (PM) and column aerosol optical thickness (AOT) is examined. It is found that a strong linear correlation exists between PM and AOT, and better correlation is obtained for the aerosols with the same origin, such as anthropogenic aerosols and dusts, rather than overall. The derived regression lines between PM2.5 and AOT highlight the possibility that the PM2.5 concentration can be estimated from the AOT, and vice versa. As a result, a distribution map of PM2.5 has been obtained by using AOT values derived from Terra/MODIS data observed in April 2006 over East Asia.
In this study, we focus on the investigation of the airborne behavior of respirable particulate matters containing Japanese cedar pollen allergen Cry j 1 exfoliated from the Ubisch bodies on the pollen surfaces and Cry j 2 comprised in the starch granules within the pollen. The airborne Japanese cedar pollens were counted, and at the same time, the Cry j 1 and Cry j 2 particles were collected and determined in different particle sizes at the urban site (Cooperative Research Center of Saitama University) during daily sampling periods of the most severe pollination season of FY 2005 in Saitama, Japan. Morphological observation of Ubisch bodies exfoliated from pollen and ruptured pollens was performed with a scanning electron microscope. Moreover, the existing evidences of visualized Cry j 1 and Cry j 2 allergen particles below 1.1μm were also sensitively found by an immunofluorescence technique with a fluorescence microscope. Simultaneously, the high concentrations of Cry j 1 and/or Cry j 2 were determined in the fine particle sizes below 1.1μm. It was suggested that airborne respirable particulate matters containing Cry j 1 and Cry j 2 play a key role in the increasing incidence of asthma in the lower respiratory tract. Furthermore, although the release mechanisms of Cry j 1 and a Cry j 2 particles may be differed, the daily variation delays in the peaks of Cry j 1 (or Cry j 2) concentrations compared to the peaks of airborne pollen counts were observed since the fine particles were suspended in the atmosphere over a longer period of time after released. It is important to observe and determine the size distribution of airborne Japanese cedar pollen allergen particles in the long-term sampling research continually, and to elucidate the allergen particle release mechanisms. In the future, we should investigate the chemical, physical and biomedical combination effects on Japanese cedar pollen allergens, and have to consider proposing a new forecast informational system of the Japanese cedar pollen and their allergen particle variations.
A novel portable particle sampler with a polymer honeycomb film filter has been developed. The high aperture ratio of the honeycomb film reduces the flow resistance and enables high-volume sampling as a portable sampler. The pore size of the honeycomb film is very uniform so that it can selectively capture aerosol particles with a specific size. Because each aerosol particle is captured separately on the surface of the filter, captured particles can be readily observed without separation and extraction preprocessing. It was examined that even transparent fibers such as rockwool and asbestos can be observed with optical microscopy without preprocessing. Preliminary field sampling of sea salt particles and bioaerosols showed that the developed honeycomb film filter sampler was very useful for the analysis of single particles.