Average mass median diameter

Table 1 Average mass median diameter for fluids nebulized in a Pari LC nebulizer...

Table IV Elemental Average Mass Median Diameter, dp...

Figure 6 shows observed and model calculated deposition at the top of the slash pine canopy for Trial 6. The mass median diameter drop for Trial 6 was 583 ym. The ratio of the average measured deposition to the average model-calculated deposition is about 1.3 for this trial. Observed and model calculated... 

Choice of which average diameter to use in a given situation depends on how the diameter was measured or how it is to be used. For the case where aerosol mass is measured and the fractions collected are associated with specific particle diameters, the resulting average value is the mass median diameter. In studying chemical reaction rates, the volume-surface mean diameter may be more important than just the arithmetic mean or geometric number mean. 

P3). The average mass median aerodynamic diameter was 3.55 0.07 pm with the geometric standard deviation of 2.55. The test was also conducted to compare the device performance with other small-volume nebulizers,and found to be more efficient in the delivery rate (mass out per minute) than that of other SVNs. 

Table 22.4 presents typical aerosol size distributions and concentrations based on measurements in many locations, including mass median diameters, Dpg, geometric standard deviations, ag, and volume concentrations V((Mm cm ) of the nuclei, accumulation, and coarse particle modes of eight classifications of aerosol. We note only a small variability in the accumulation and coarse mode size distributions for the variety of aerosol classes (excluding the marine aerosol). The average specifications for the accumulation and coarse... 

Winkler et al. (1998) reported that the activity size distribution of Pb in ambient aerosols was unimodal (log-normal) and associated with submicron aerosols of about 0.5 to 0.6 pm. On average, the activity median aerodynamic diameter, AMAD, of Pb-aerosols (0.53 pm) has been found to be significantly lower than the average mass median aerodynamic diameter, MMAD (0.675 pm), and higher than or at most equal to the respective surface median aerodynamic diameter, SMAD, (0.465 pm) of the aerosols SMAD < AMAD < MMAD. Variation of the atmospheric processes resulted in a variability of the activity median aerodynamic diameter, AMAD, between 0.28 and 0.74 pm for Pb. While in the winter period (October to April) the AMAD of Pb averaged 0.595 pm, in the summer period Pb was associated with significantly smaller aerosols (AMAD 0.43 pm). 

In certain mass-transfer operations, such as spray columns, the Sauter mean diameter is a useful quantity to know. However, in studies of droplet erosion or droplet separation, the volume or mass median diameter is more physically meaningful. This volume-average (median) drop diameter is related to the Sauter-mean diameter through the following approximation (AIChE, 1978). 

Count mean diameter, d Diameter of average mass, Mass median diameter, MMD Mass mean diameter, d ... 

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

Pb-212 vs S0%- LPI Distributions. Figure 3 presents a summary of the average Pb-212 AMADs and SOj MADs (mass median aerodynamic diameters) determined from a series of LPI measurements made during the period January to October, 1985. The Pb-212 data were derived from collections made at the same time as S0jj and from measurements made to compare Pb-212 vs Pb-214. The mean aerodynamic diameter of Pb-212 was about three times smaller than SoJ . Much less sulfate was found in the aerosol fraction below 0.08 um, compared with Pb-212. While Pb-212 was largely absent above 0.52 um, about 20% of the SoJ occurred above this size. 

The Mass Median Aerodynamic Diameter (MMAD) was reported as a lower limit of 0.8 pm and an upper limit of 1.2 pm for an average of 1.0 pm (pg 33 Hartman 1990). The Geometric Standard Deviation (GSD) was reported as a lower limit of 1.2 pm and an upper limit of 1.5 pm for an average of 1.35 or 1.4 pm. The Regional Deposited Dose Ratio (RDDR) from Table HI under the ER (Extrarespiratory effects) column is... 

There are a number of different mean or median values which can be defined for a particle size distribution. These means or medians are useful depending on where the data came from or how the data are to be used. For example, the diameter of average mass (volume) can be defined as representing the diameter of a particle whose mass (volume) times the number of particles gives the total mass (volume) of all the particles. Similarly, the diameter of average surface represents the diameter of a particle whose surface times the number of particles gives the total surface. 

Figure 3. An example of the log-normal distribution function in normalized linear form for CMD = 1.0 and Og = 2.0, showing the mode, median and mean of the size distribution, the surface area distribution median and mean diameters, the mass distribution median and mean diameters, and the diameter of average mass. Reproduced with permission from Raabe OG (1970). Generation and characterization of aerosols. In Inhalation Carcinogenesis (MG Hanna, P Nettersheim and JR Gilbert, eds), pp. 123-172. Proceedings of a Biology Division, Oak Ridge National Laboratory Conference. Oak Ridge, TN, USA US Atomic Energy Commission...

Using the data on radon decay product aerosols, Papastefanou and Bondietti (1991) reported a mean residence time, xr, of 8 days for aerosols of 0.3-pm activity median aerodynamic diameter (AMAD) size as determined from Bi/ Pb activity ratios. From the decay scheme of 2 Po T /2 = 3.05 min), because of the relatively short half-lives of the product radionuclides after two a-decays and two /S-decays, Pb-aerosols are produced. From 32 experiments for radon decay product aerosols ( °Pb-aerosols), Papastefanou and Bondietti (1991) calculated average values of fractions F and F2 of about 76.11 and 21.32, respectively. From 12 measurements of sulfate aerosols, Bondietti and Papastefanou (1993) calculated in the same manner average values of fractions F and F2 of about 68.67 and 12.63, respectively. According to Equation (4.12) and the above mentioned data, a mean residence time, xr, SO , of about 12 days would apply to sulfate aerosols of 0.3-pm mass median aerodynamic diameter (MMAD) size. 

We consider here three types of equations that convert the CMD to (1) another median diameter, (2) a weighted mean diameter, and (3) a diameter of average property. Although these equations are written for CMDs, they can be combined to convert any type of average diameter to any other type of average diameter. The examples diat follow are for the most common case, conversions between number and mass distribution. Analogous equations can be written for any moment distribution, such as the distribution of surface area or of settling velocity. 

A frequency function has a constant value between 1.5 and 6.5 pm and is zero elsewhere. Determine the arithmetic mean, number median, diameter of average mass, and surface mean diameter. Hint Divide the distribution into five equal intervals with midpoints at 2, 3, 4, 5, and 6 pm.]... 

Average Particle Size A powder has many average sizes hence it is essential that they be well specified. The median is the 50 percent size half the distribution is coarser and half finer. The mode is a high-density region if there is more than one peak in the frequency cui ve, the distribution is said to be multimodal. The mean is the center of gravity of the distribution. The center of gravity of a mass (volume) distribution is defined by. Xyw = X XdV/X dV where dV = X dN dV is the volume of dN particles of size X This is defined as the volume-moment mean diameter and differs from the mean for a number or surface distribution. 

---