Aerosol geometrical standard deviation

Aerosol, monodisperse An aerosol with a size-distribution function described by a geometrical standard deviation less than 1.15. If the deviation is between 1.15 and 1.5, it is classified as a quasi-mono-disperse aerosol. 

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. 

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)...

Table II. Summary of Mean Monthly Activity Median Aerodynamic Diameters (AMAD) and Geometric Standard Deviations (tfg) of Radon and Thoron Daughter Size Distributions in Ambient Aerosols...

Fig. 1. Deposition of inhaled particles of different sizes (mass median aerodynamic diameters) in the three regions of the respiratory tract. Each shaded area indicates the variability of deposition when the aerosol distribution parameter, o, (geometric standard deviation) was varied from 1.2 to 4.5. The assumed tidal volume was 1450 cm3. (Reproduced from Health Physics, vol. 12, pp. 173-207,1966 by permission of the Health Physics Society).

Boecker, 1973) exposed to other radioactive aerosols was also reviewed. An analysis of the data from both studies suggested that for beagles exposed by inhalation to radioactive 144Ce aerosols, individuals in the population would receive radiation doses to a given organ within a fog-normal distribution characterized by a geometric standard deviation of 2. 

Both from deposition studies and force balances it can be derived that the optimum (aerodynamic) particle size lies between 0.5 and 7.5 pm. Within this approximate range many different subranges have been presented as most favourable, e.g. 0.1 to 5 pm [24], 0.5 to 8.0 pm [25], 2 to 7 pm [26] and 1-5 pm [27-29]. Particles of 7.5 pm and larger mainly deposit in the oropharynx [30] whereas most particles smaller than 0.5 pm are exhaled again [31]. All inhalation systems for drug delivery to the respiratory tract produce polydisperse aerosols which can be characterized by their mass median aerodynamic diameter (MMAD) and geometric standard deviation (oq). The MMAD is the particle diameter at 50% of the cumulative mass curve. 

An advantage of applying the log-normal distribution to atmospheric aerosols is that the value of the geometric standard deviation, crg, is the same for a given sample for all types of distributions—count, mass, surface, and volume. It is only the value of the geometric mean diameter that changes, depending on the... 

A monodisperse aerosol is one with a narrow size distribution, which, for log-normal-distributed particles, usually means a geometric standard deviation of about 1.2 or smaller. Monodisperse particles are expected to have simple shapes and uniform composition with respect to size. A polydisperse aerosol, on the other hand, is one containing a wide range of particle sizes, but which may otherwise be homogeneous in terms of the basic physical and chemical properties that are not related to size. The term heterodisperse is also used occasionally this describes aerosols varying widely in physical and chemical characteristics, as well as size. 

In order to overcome the inherent problem associated with pulmonary aqueous solution and dry powder aerosols, Choi et al. [2] developed an ethanol suspension of insulin for inhalation, in which the solid insulin is suspended in ethanol and aerosolized with a commercial compressor nebulizer. The aerosol insulin particles were found to be 1.5 pm, with a geometric standard deviation of 1.3 pm. Exposure of rats to 10 mg/mL insulin aerosol resulted in a drastic fall in blood glucose and a marked rise in serum insulin level. The bioavailability of insulin/ethanol aerosol was 33% relative to SC injection, and comparable to that of insulin aerosols in aqueous solution and dry powder form. No acute toxic effects were detected in the rat lungs or airways [2]. 

The geometric standard deviation (GSD) is defined as the size ratio at 84.2% on the cumulative frequency curve to the median diameter. This assumes that the distribution of particle sizes is lognormal. A monodisperse, i.e. ideal aerosol, has a GSD of 1, although in practice an aerosol with a GSD of <1.22 is described as monodisperse while those aerosols with a GSD >1.22 are referred to as poly dispersed or heterodispersed. 

Example 8.6 An aerosol made up of unit-density spheres is lognormally distributed with a geometric mean diameter of 2.0 pm and a geometric standard deviation of 2.2. Calculate the respirable fraction of this aerosol as sampled by a sampler which follows the BMRC curve and a sampler which follows the ACGIH curve. 

For the case of a lognormal aerosol having a geometric mean diameter of dg and geometric standard deviation of ag,... 

We routinely use nose-only inhalation exposure of B(a)P aerosol to evaluate the consequence of prenatal exposure to this toxicant on physiological and behavioral endpoints. The properties of this B(a)P aerosol are shown in Figure 17.4. The aerosol typically exhibits a trimodal distribution with a 93% cumulative mass less than 5.85 pm, 89% cumulative mass less than 10 pm, 55.3% cumulative mass less than 2.5 pm, and 38% less than 1 pm. Fifty-five percent of the aerosol generally has a cumulative mass less than PM2.5 and the mass median aerodynamic diameter (MMAD) + geometric standard deviation for this mode is consistently 1.7 =E 0.085 pm. For several years we employed a rat model exposing timed pregnant dams to inhalation concentrations of 25, 75, and 100 pg/m. ... 

Aerosol size has an effect on the lung dose. Fine particles breathed through the mouth or the nose from lOOnm to 1,000 nm median size had 5-20 nGy per becquerel. Below 100 nm, this number more than doubled at 25-65 nGy per becquerel at 20 nm median size. Median sizes had an approximate geometric standard deviation of 2, so that the 95% confidence interval of particle sizes ranged from 0.25 to 4 times the stated median size. Very small particles deposited more efficiently in the airways. Lung cancer was related to radiation dose. These dose estimates are important determinants of lung cancer. 

Aerosol properties, such as particle size distribution, aerosol velocity, and hygroscopicity, affect aerosol deposition in the human lungs. Aerosol size distribution, including mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD), is one of the most important variables in governing the site of droplet or particle deposition in the lungs. ... 

An aerosol rarely consists of particles that are the same size, and usually a distribution of sizes around a mean is observed. The observed data may be fitted by statistical approximation to a distribution. The number of particles in a size range when plotted against the logarithm of the particle diameters frequently exhibit a normal (Gaussian) distribution. This is known as a log-normal distribution and is described by a parameter known as the geometric standard deviation. Theoretically, a monodisperse aerosol will exhibit a geometric standard deviation of 1 in practice, however, an accepted limit is 1.2 [6]. 

Fnrthermore, for dosage consistency, there is a need for an aerosol formulation to be monodispersed [4]. The particle size distribution of an aerosol is defined by its geometric standard deviation (GSD). The GSD is the ratio of particle diameters at 84% and 50% cnmnlative mass of particles or the ratio of the particle diameters at 50% and 16% cnmnlative mass of particles when the cumulative mass of particles is plotted against the eqnivalent diameter on a log-probability scale following particle size analysis nsing either impactors or laser diffraction instruments. 

Let the geometric mean (mg) of the distribution of particle sizes in an aerosol be 1.0 pm. Let the geometric standard deviation (erg) be 2.0 pm. The arithmetic median (usually referred to simply as the median) of the distribution is then 1.0 pm. 

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