Particles geometric mean diameters

A word of caution is also in order with respect to assigning a particular particle to the fine or coarse particle modes. Since the size distributions can generally be described as log-normal, they do not have sharp cutoffs. A few particles at the top end of the fine mode distribution will have diameters larger than 2.5 [jlm and a few at the bottom end of the coarse mode will have diameters smaller than this. For example, as Lodge (1985) points out, for a coarse particle distribution with a geometric mean diameter of 15 fim and a geometric standard deviation of 3, about 5% of the particles will have diameters below the 2.5-gm fine particle cutoff. This may be responsible for observations that while Si and Ca dominate the coarse particle mode, they are also often found at significant levels in fine particles (e.g., see Katrinak et al., 1995). 

The data were obtained from the samples summarized in Table L The fallout samples were separated into particle-size classes by standard sieves for particles larger than 44p and by the Roller analyzer for particles smaller than 44fi. In the sequel the size classes are characterized by their geometric mean diameters. The larger size classes of the Tewa sample were separated mechanically under the microscope into spherical and irregular fractions. Very few spheres could be found below the 177-/x class. The ratio of active to inactive particles was measured auto-... 

Table 5—Method of Determining the Geometric Mean Diameter of 245 Particles Measured by Means of an Optical Micrometer...

If particle sizes are initially distributed lognormally, an expression can be written for K in terms of the geometric mean diameter dg and geometric standard deviation crg ... 

The characteristic data of particles are given by the mode diameter (MD) as the most frequent size of a particle population, the geometric mean diameter (OMD) of the particles and the total number concentration (TNC) as the total amount of particles over the whole measured range. The TNC is based on the flue gas volume at a standard oxygen content of 13%. 

The combustion chamber of the moving grate boiler system was run over a wide range ofbum rates, starting from 150 kW up to 600 kW. The analysis of particle emissions such as particle diameter or total number concentrations (TNC) showed only little variations with the process parameters (Fig. 3). Similar to the 70 kW burner system, all test runs resulted in mode diameters most frequent size diameter) of 100 nm. The geometric mean diameter (GMD) has been analysed in the range of 90.45 nm up to 95.0 nm. The total number concentration (TNC) was between 2.8IE-i-7 and 5.12E-I-7, depending on excess air supply. 

Figure 2 presents the particle emission size distribution for Tests 2 and 4 measured with SMPS. It is possible to verify the presence of one only mode in the submicron size range, although other nanometric modes could exist below 0.01 micron. The detected mode is located in the 0.2 to 0.3 micron range, and its geometric mean diameter (GMD) is approximately 0.2 pm. Notice that, although the particle... 

Figure 5. Particle size distribution. Geometric mean diameter, 11.62 fjm median, 11.94 yjn mode, 13.07 fim and standard deviation, 1.59 ixm.

In Tables III and IV are listed the values of the average size of the dispersed particles (S) for the PS/PMMA specimens from our earlier work and the PS/P(MMA-S) specimens under consideration here, respectively. The average size is defined, perhaps somewhat arbitrarily, as the average of the geometrical mean diameter of the particles in a given representative area. Some care must be taken to avoid obtaining underestimates of S (39) usually the standard deviation of our values is within 5%, and never greater than 10%. 

Geometric mean diameters (dg ) and geometric standard deviations (ag) of the particle size distribution obtained with the Coulter Counter in inert and swelling media and relevant swelling indexes. 

The geometric mean diameters and geometric standard deviations of the particle size distributions of Explotab and P Cyclodextrin polymer fractions are given in Table 3. The results relative to Ac-di-Sol fractions are not reported since their particle size distribution in inert medium was rather broad, possibly owing to the critical fiber-like shape, and did not fit any distribution model. 

Figure 5 Distribution of coarse, accumulation, or fine, and nucleation or ultrafine mode particles by three characteristics DGV, geometric mean diameter by volume DGS, geometric mean diameter by surface area DGN, geometric mean diameter by number. (From Ref 107.)...

Three particle modes were observed in the size range investigated in this study. One mode with a geometric mean diameter of 5.5 nm was correlated with solar radiation, (i.e., with particle formation by photochemistry). Another mode (Dp = 24 nm) correlated mostly with peaks in car traffic (i.e., minimums during nights and weekends and maximums during rush hour on working days). A third mode Dp = 50 nm), however, did not show a dependency on the time of day. 

Figure 3 Measured volume-size distribution showing fine-mode and coarse-mode particles and the nuclei and accumulation modes within the fine-particle mode. DGV, geometric mean diameter by volume equivalent to volume median diameter, and Og, geometric standard deviation, are shown for each mode. Also shown are transformation and growth mechanisms (e.g., nucleation, condensation, and coagulation). (From Ref 138.)...

---