Particles respirable size range

Particles in the respirable size range, i.e. about 0.5—7 pm, will, once dispersed, remain airborne for extended periods. Indeed since they are sensitive to slight air currents they may be permanently suspended. 

The relationship of particle size to molecular composition is highly significant. (2). Particles below 1-3 fun (submicron size class) in diameter are considered respirable by animals, in that this material can reach the lower alveoli of the lung. Particle size information may be used to determine the sources of various atmospheric pollutants. Particulate matter formed from gaseous pollutants tends to be found in the less than the 1-3 /nm particle diameter size range. Supermicron sized particles (particles greater than 1- 3 typically originate from primary emission sources, (i.e., stack emissions, vehicles, soil). 

On the other hand, particles from fossil fuel combustion and gas-to-particle conversion are generally much smaller (< 2.5-/Am diameter) and fall in the respirable size range. These particles can reach the alveolar region where gas exchange occurs. This region is not coated with a protective mucus layer, and here the clearance time for deposited particles is much greater than in the upper respiratory tract hence the potential for health effects is much greater (Phalen, 1984). 

However, even with this limited data set it was possible to state that emissions from high-temperature sources are contained in particles which are in the (respirable) size range that can be trapped in the respiratory region. If the data contained in Table III and Table IV are compared for the elements that both techniques could detect (Fe and Zn), then the total atmospheric loading for Fe is 0.108 g/m by NAA and 0.098 g/m by AAS and for Zn is 0.037 g/m by NAA and 0.028 g/m by AAS. These samples were obtained on different days and yet the total loadings were comparable. However, the distribution of metals in the various particle... 

The formulation of DPIs is dependent on the nature of particles employed in the formulation. The delivery of dry powder products is dependent on effective dispersion of particles in respirable size ranges. This has been brought about by blending with carrier... 

The principal hazard involved in the handling and use of many fillers is inhalation of airborne particles (dusts) in the respirable size range, ie, 10 /tm and below. Filler dusts may be classified as nuisance particulates, fibrogens, and carcinogens. Nuisance particulates are dusts that have a long history of little adverse effect... 

Because a filter sample includes particles both larger and smaller than those retained in the human respiratory system (see Chapter 7, Section III), other types of samplers are used which allow measurement of the size ranges of particles retained in the respiratory system. Some of these are called dichotomous samplers because they allow separate measurement of the respirable and nonrespirable fractions of the total. Size-selective samplers rely on impactors, miniature cyclones, and other means. The United States has selected the size fraction below an aerodynamic diameter of 10 /xm (PMiq) for compliance with the air quality standard for airborne particulate matter. 

Dust Airborne solid particles (an aerosol) that range in size from 0.1 to 50pm and larger in diameter. A person with normal eyesight can see dust particles as small as 50 pm in diameter. Smaller airborne particles cannot be seen unless strong light is reflected from the particles. Dust of respirable size (below 10 pm) cannot be seen without the aid of a microscope. 

Watson [72] developed a graticule designed specifically to measure particles in the 0.5 to 5 pm (respirable dust) size range. 

The particle size range for the respirating mechanism for each of these is shown in Table 16. 

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