Size Distributions of Atmospheric Aerosol Particles

Meszaros a., On the size distribution of atmospheric aerosol particles of different composition. Atmos. Environ. , 11, 1075-1081 (1977). 

Concentration and size distribution of atmospheric aerosol particles... 

Size distribution of atmospheric aerosol particles under various conditions, (f). urban (2). continental (3) tropospheric back ground (4) continental at 3000 m above inversions N total number of particles with radius larger than 0.03 fiw. (Data of A. Meszaros)... 

Curve J of Fig. 28 represents the size distribution of atmospheric aerosol particles obtained by A. Meszaros and Vissy (1974) from samples collected on membrane filters over the oceans of the Southern Hemisphere. The samples were evaluated by optical and electron microscopy in the radius range of 0.03-64 /tm8. The total concentration of these particles is also shown. It can be seen that the maximum of the distribution occurs around 0.1 /Jir> radius, a value in the range of the... 

A method for estimating the residence time of tropospheric aerosol particles associated with the cosmic-ray produced radionuclides, such as Be, is based on the aerosol particle growth rate, which is the change of particle diameter with time, which was estimated to be 0.004 to 0.005 pmh (McMurry and Wilson, 1982) and the difference between the activity median aerodynamic diameter, AMAD, of a radionuclide, e.g. Be, and the size of the Aitken nuclei in the size distribution of the aerosol particles, which is 0.015 pm (NRC, 1979). The AMAD of all radionuclides is in the accumulation mode of the size distribution of atmospheric aerosol particles which ranges between 0.1 and 2.0 pm (NRC, 1979 Papastefanou and Bondietti, 1987). 

The climate effects of atmospheric aerosol particles are a matter of continuous interest in the research community. The aerosol-climate effects are divided into two groups The direct effect represents the ability of the particle population to absorb and scatter short-wave radiation - directly affecting the radiation balance. These direct effects depend primarily on the aerosol optical properties and particle number size distribution, as the particle size significantly affects the scattering efficiency of... 

Meszaros, A. and Vissy, K., 1974 Concentration, size distribution and chemical nature of atmospheric aerosol particles in remote oceanic areas. J. Aerosol Sci. 5, 101-110. 

Figure 2.20 shows an example of a bimodal particle size distribution for aerosol particles released from an industrial process that produces fumes and dusts [10]. Figure 2.21 shows some more complicated volume distributions for atmospheric aerosol particles (NARSTO [126]). 

Sweepout and interception most efficiently remove larger particles (particle diameter > 1 pm). Diffusion is most efficient for very small particles (particle diameter < 0.1pm). Consequently, very fine and very large aerosol particles are efficiently removed from the containment atmosphere by sprays. There is, however, an intermediate size of particle that is minimally affected by sprays. The decontamination of the atmosphere of these intermediate sized particles is increased by decreasing the size of the spray droplets, which are typically between 250 and 2000 pm in diameter. Because of the particle size dependence of spray effectiveness, the spray not only changes the concentration of particles in the atmosphere, it also changes the size distribution of these aerosols. The residual aerosol has a narrow distribution of sizes centered around the size minimally affected by the spray. 

These quantities depend strongly on the different interaction processes of the decay products in air like attachment to aerosol particles, cluster formation, neutralisation of the cluster, and plateout on surfaces and on composition and behaviour of the atmospheric air (number concentration and size distribution of the aerosol, humidity, trace gases, turbulence). 

Particles in the atmosphere come from different sources, e.g., combustion, windblown dust, and gas-to-particle conversion processes (see Chapter 6). Figure 2-2 illustrates the wide range of particle diameters potentially present in the ambient atmosphere. A typical size distribution of ambient particles is shown in Fig. 2-3. The distribution of number, surface, and mass can occur over different diameters for the same aerosol. Variation in chemical composition as a function of particle diameter has also been observed, as shown in Table 4-3. 

In exposures of humans to artificially generated aerosols, where the information is to be relevant to ambient aerosols, several factors are important the particle diameter distribution must be fairly constant and fall within size ranges typical for the given compound in the ambient air, the chemical composition of the aerosol must be stable and predictable, and the electric charge distribution of the aerosol must simulate that of normal atmospheric aerosols. 

Sverdrup, G.M., "Parametric Measurement of Submicron Atmospheric Aerosol Size Distributions " Ph.D. Thesis, Particle Technology Laboratory University of Minnesota, Minneapolis 55455, 1977. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

To better understand the effects of atmospheric processes (reactions, gas-particle partitioning, etc.) on the size distributions of PAHs in ambient aerosols, Venkataraman and Friedlander (1994b) carried out measurements of gases and particles during winter and... 

Particle Measurements. A variety of instruments is available for measuring the number density and size distribution of particles sampled from airborne platforms. This discussion is restricted to instruments that measure particles smaller than 50 xm (cloud droplets and aerosol particles) because these particles are of most interest to atmospheric chemists. 

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