Size distribution ultrafine range

It has been found that the "unattached" fraction is an ultrafine particle aerosol with a size range of 0.5 to 3 nm. In order to initiate studies on the formation mechanism for these ultrafine particles, a series of experiments were made in the U.S. Bureau of Mines radon chamber. By introducing SO into the chamber, particles were produced with an ultrafine size distribution. It has been found that the particle formation mechanism is supressed by the presence of radical scavengers. These experiments suggest that radiolysis following the decay of Rn-222 gives rise to the observed aerosol and the properties of the resulting aerosol are dependent on the nature and the amount of reactive gas present. 

Polymerization in microemulsions allows the synthesis of ultrafine latex particles in the size range of 5 to 50 nm with a narrow size distribution [33], The deposition of an ordered monolayer of such spheres is known to be increasingly difficult as the diameter of such particles decreases [34], Vigorous Brownian motion and capillary effects create a state of disorder in the system that is difficult... 

As we have seen in our earlier discussion of the size distribution of tropospheric particles, the chemical components are not generally distributed equally among all sizes but, rather, tend to be found in specific size ranges characteristic of their source. Generally, the smallest ultrafine particles are produced by homogeneous nucleation and hence tend to contain secondary species such as sulfate and likely organics (see Section A.2). Particles in the Aitken nuclei range are produced... 

In a similar study, Allen and co-workers (1996) determined the particle size distribution for 15 PAHs with molecular weights ranging from 178 (e.g., phenan-threne) to 300 (coronene) and associated with urban aerosols in Boston, Massachusetts. As for BaP in the winter (Venkataraman and Friedlander, 1994b), PAHs with MW >228 were primarily present in the fine aerosol fraction (Dp < 2 /Am). A study of 6-ring, MW 302 PAH at the same site showed bimodal distributions, with most of the mass in the 0.3- to 1.0-/zm particle size size range a smaller fraction was in the ultrafine mode particles (0.09-0.14 /xm) (Allen et al., 1998). For PAHs with MW 178—202, the compounds were approximately evenly distributed between the fine and coarse (D > 2 /am) fractions. Polycyclic aromatic hydrocarbons in size-segregated aerosols col-... 

Concentration of particles in the air as well as particle size distributions can be considered either in terms of particle number or mass. In terms of number, the vast majority of airborne particles are in the ultrafine range. For example, in urban outdoor air where motor vehicle emissions are a dominant pollution source, over 80% of particulate matter in terms of number is in the ultrafine range [17]. Since outdoor particles contribute significantly to indoor particle concentrations, also in indoor air particle number concentration is usually dominated by the smallest particles. However, most of the mass of airborne particles is associated with large particles since the mass of ultrafine particles is often very small in comparison with the mass of larger particles. The particle surface area in turn is largest for particles somewhat above the ultrafine size range. 

GCC grades available for plastics are classified based on their particle size distribution (psd) and type of surface treatments. Ultrafine grades have a median particle size of about 0.7-2 pm. Fine grades are between 3 and 7 pm and surface treated have median particle size (based on untreated material) ranging from 1 to 3 pm [9]. Grades of different particle sizes are recommended depending on the polymer, the intended application, and the fabrication method. PCC grades can be submicron in median particle size. 

P. E. Plantz. Ultrafine particle size measurement in the range 0.003 to 6.5 micrometers using the controlled reference method. In T. Provder, ed.. Particle Size Distribution III Assessment and Characterization, ACS Symp. Ser. 693, 1998, pp. 103-129. 

The size distributions of colloidal suspensions of nanoparticles 74 nm to 14 nm in diameter are analyzed on-line. The sols are first diluted in water seeded with enough TFA to attain electrical conductivities in the range of 0.01 S/m. The solution is then finely dispersed into an atmosphere of CO2 via a Taylor cone-jet. The resisting electrospray of ultrafine droplets dries, transferring the solution particles virtually uncontaminated into the gas. There they are sized by means of a differential mobility analyzer and an inertial impactor of unusually high resolution. The technique is first tested successfully with previously calibrated monodisperse polystyrene latex (PSL) spheres 74 to 21 nm in diameter. It is then used to size a solution of colloidal silica with particle diameters nominally between 10 and 14 nm. 

Plantz, P. E., Ultrafine Particle Size Measurement in the Range 0.003 to 6.5 micrometers Using the Controlled Reference Method, in Particle Size Distribution III, Ed. Provder, T., ACS Symp. Series 693, American Chemical Society, Washington D.C., 1998, Chpt.9, pp. 103-129. 

Atmospherie aerosol particles are principally divided into fine and coarse partieles. The fine-particle-size range covers geometric particle diameters (Dp) 1 >Dp > 1000 nm. Particles with Dp > 1 pm are called coarse partiele. Fine particles are also defined as Dap > 2.5 pm (e.g., by inhalation toxieologists for which Dap is defined as the aerodynamic particle diameter). The entire number-size distribution can be principally described by four different aerosol particle modes (Table 2). Fine particles belong to the nucleation (ultrafine), the Aitken, or the accumulation mode (1). The fourth mode is the coarse particle mode. 

---