Count median diameter

Theoretical calculations of unattached fractions of radon progeny require prediction of an attachment coefficient. Average attachment coefficients for aerosols of various count median diameters, CMD, and geometric standard deviations, ag, are calculated using four different theories. These theories are ... 

Theoretical calculations of unattached fractions of radon or thoron progeny involve four important parameters, namely, 1) the count median diameter of the aerosol, 2) the geometric standard deviation of the particle size distribution, 3) the aerosol concentration, and 4) the age of the air. All of these parameters have a significant effect on the theoretical calculation of the unattached fraction and should be reported with theoretical or experimental values of the unattached fraction. 

Figures 3 and 4 show the variation of the attachment coefficient with count median diameter for the diffusion, kinetic, hybrid and kinetic-diffusion theory for geometric standard deviations of 2 and 3 respectively.

In Figs. 6 and 7 the attachment coefficient is plotted against the geometric standard deviation using the four theories, for count median diameters of 0.2 ym and 0.3 ym respectively. 

Theoretical unattached fractions of RaA using average aerosol concentrations and count median diameters as found in track and trackless Canadian uranium mine are presented in Table III. The reported uranium mine aerosol properties are N 120,000 particles/cm3 and CMD = 0.069 ym for a trackless mine and N =... 

An aerosol size distribution can, therefore, be described in terms of the count median diameter, d, and the geometric standard deviation, a These parameters were obtained from experimental data using a diffusion battery method (Busigin et al., 1980). A diffusion battery is an assembly of a number of cylindrical or rectangular channels. The relative penetration of aerosols through different sizes of diffusion batteries at specified flow rates allows the aerosol size distribution to be calculated. 

Table IV. Activity and Aerosol Size Distributions, Count Median Diameter (CMD) and the Geometric Standard Deviation (indicated in brackets)...

Count median diameter. Geometrie standard deviation. 

Figure 2 Representative log-normal particle size distribution. The values in parentheses are based on a count median diameter of 1.0 p.m and a o-g of 2.0. (With permission of Health Physics.)...

Fig. 6 The dependence of particle count median diameter (CMD) and concentration on time...

Here, CMD stands for count median diameter, i.e. m.g in the equations given above. 

MMD and area median diameter (AMD) are the geometric means of the mass and area distributions, respectively. In the same way that the arithmetic mean and mode were calculated from nig (count median diameter), so equivalent values can be calculated from the MMD and AMD. 

Count mean diameter (0.49 urn) Count median diameter (0.41 urn)... 

Having predicted the deposition of particles of different sizes, the Task Force calculated the predicted pattern of deposition of particles from polydisperse aerosols of known count median diameter and ag. The results of these most important calculations are shown in Table 10. The importance of this table cannot be overestimated ... 

Count median diameter (CMD) That diameter where 50% of the particle count (number) is both above and below the diameter. 

For the count distribution, the geometric mean diameter dg is customarily replaced by the count median diameter, or CMD. The geometric mean is the arithmetic mean of the distribution of In d, which is a symmetrical normal distribution, see Fig. 4.8, and hence, its mean and median are equal. The median of the distribution of In dp is also the median of the distribution of dp, as the order of values does not change in converting to logarithms. Thus, for a lognormal count distribution, dg = CMD. The frequency function can be expressed as... 

This range is asymmetrical and goes from CMD/oJ to CMD x aj. For Cg = 2.0, 95% of the particles have sizes between one-fourth and four times the count median diameter. 

FIGURE 4.16 Ratios of mass median diameter and diameter of average mass to count median diameter versus geometric standard deviation. 

An aerosol has a lognormal particle size distribution with a mass median diameter of 10.0 pm and a geometric standard deviation of 2.5. What is the count median diameter Assume = 3000 kg/m [3.0 g/cm ]. 

Deteimine the mass median diameter and geometric standard deviation of this distribution using log-probability graph paper. Use the appropriate conversion equation to determine the count median diameter. 

An aerosol with a lognormal size distribution has a count median diameter of 2.0 (xm and a geometric standard deviation of 2.2. If the mass concentration is I.O mg/m, what is the number concentration Assume spherical particles with Pp = 2500 kg/m [2.5 g/cm ]. 

Consider an aerosol with a lognormal size distribution (GSD = 1.8). The size distribution is in a range where slip correction can be neglected and Stokes s law holds. If the diameter of the particle of average settling velocity is determined to be 6.0 pm, what is the count median diameter ... 

Figure 4 (A, B) Number-frequency distribution and (C) cumulative number distribution of an aerosol of unit-density spheres. Indicated are the count median diameter (CMD), the surface median diameter (SMD), and the mass median diameter (MMD) of the number-frequency distribution. The 16, 50, and 84% size cut of the cumulative number distribution are shown. For further explanation, see text.

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