Mean mass aerodynamic diameter MMAD

Panicles entrained in the airstream deposit along the airway as a function of size, density, airstream velocity, and breathing frequency. Sizes of rougjily spherical or irregularly shaped particles arc commonly characterized by relating the settling velociiy of the particle to that of an idealized spherical particle. For example, an irregular particle which settles at the same rate as a 5 pm spherical particle has a mean mass aerodynamic diameter (MMAD) of. 5 pm. Since spherical particle mass, is a function of particle diameter, J... 

Mean mass aerodynamic diameter (MMAD) Mean diameter of theoretical... 

Thus, Eqs. (2) and (3) enable us to convert the volume-equivalent particle size distribution into aerodynamic-equivalent distribution for any flow regime. The characteristic mean diameters are dy (volume geometric) and (volume aerodynamic). Although dp is numerically close to the mass-median aerodynamic diameter (MMAD) often used for the aerosols, it is better defined for asymmetrical distribution, so often observed for respiratory powders. 

Baldwin et al. (2001) exposed 6-month-old Fischer 344 rats to room air or JP-8 aerosols alone or to JP-8 and then aerosolized substance P, which has been shown to attenuate the effects of JP-8-induced pulmonary dysfunction and immunotoxicity in animals. Inhalation exposures were nose-only and performed 1 hr/day, 5 days/wk for 28 days. Aerosolized JP-8 with a mass mean aerodynamic diameter (MMAD) of 1.7-1.9 pm (M. Witten, University of Arizona, personal communication, 2002) was administered to the rats at... 

The activity median aerodynamic diameters (AMADs) of Pb (Table 2.3) and mass median aerodynamic diameters (MMADs) of SO (Table 2.4) determined from a series of low- pressure (LPI) cascade impactor measurements made during the period January to October (1985) by Papastefanou and Bondietti (1987) are illustrated in Figure 2.7. The Pb data were derived from measurements made at the same time as and from measurements made to compare Pb versus Pb. The mean aerodynamic diameter of Pb was about three times smaller than that of SO ". Much less sulfate was found in the aerosol fraction below 0.08 pm... 

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. 

All currently marketed inhaler devices produce polydisperse aerosols of which the individual particles have different sizes. Therefore, they cannot be characterised by a single diameter. In fact, for most solid aerosols from dry powder inhalers the particles may have different shapes too, which is the reason to characterise them with aerodynamic diameters. To be able to express polydisperse aerosols with a single parameter, the median aerodynamic diameter (MAD) was introduced. When the aerodynamic size range which covers the population of particles in the aerosol is divided into different classes and the volume or mass fraction within each size class is expressed as function of the class mean diameter, a volume or mass distribution as function of the aerodynamic diameter is obtained. This volume or mass frequency distribution can be transferred into a cumulative percent distribution of which the 50 % value corresponds with the volume or mass median aerodynamic diameter (VMAD or MMAD). This is the diameter indicating that 50 % of the total aerosol volume or mass is in larger, and 50 % is in smaller particles. When particles of all sizes in the aerosol have the same density, which is mostly the case, then VMAD equals MMAD. 

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