Aerosols charge measurement

Suzuki, S., and Tomura, M., Studies on the measurement of charges on fine particles. I. Charge measurement of tobacco and mosquito incense aerosols by a charge spectrometer, Denshi Shashin Japan) 4, No. 2, 20 (1962). 

Charged aerosols and aerosol charging Microcontamination electrostatic precipitation atmospheric electricity aerosol sampling and measurement ion-particle interactions. 

Up to this point we have considered spherical particles of a known diameter Dp and density pp. Atmospheric particles are sometimes nonspherical and we seldom have information about their density. Also a number of techniques used for atomospheric aerosol size measurement actually measure the particle s terminal velocity or its electrical mobility. In these cases we need to define an equivalent diameter for the nonspherical particles or even for the spherical particles of unknown density or charge. These equivalent diameters are defined as the diameter of a sphere, which, for a given instrument, would yield the same size measurement as the particle under consideration. A series of diameters have been defined and are used for such particles. 

Atmospheric ions are important in controlling atmospheric electrical properties and conmumications and, in certain circumstances, aerosol fomiation [128. 130. 131. 138. 139, 140. 141. 142, 143, 144 and 145]. In addition, ion composition measurements can be used to derive trace neutral concentrations of the species involved in the chemistry. Figure A3.5.11 shows the total-charged-particle concentration as a frmction of... 

The device resembles a cylindrical differential mobility analyzer (DMA) in that a sample flow is introduced around the periphery of the annulus between two concentric cylinders, and charged particles migrate inward towards the inner cylinder in the presence of a radial electric field. Instead of being transmitted to an outlet flow, the sample is collected onto a Nichrome filament located on the inner cylinder. The primary benefit of this mode of size-resolved sampling, as opposed to aerodynamic separation into a vacuum, is that chemical ionization of the vapor molecules is feasible. Because there is no outlet aerosol flow, the collection efficiency is determined by desorption of the particles from the filament, chemical ionization of the vapor, separation in a mobility drift cell, and continuous measurement of the current produced when the ions impinge on a Faraday plate. 

Although the SEMS represents a marked advance in the state of the art for measurement of aerosol size distribution, an important gap remains in current measurement technology, namely, the ability to make rapid, high-resolution measurements of the accumulation-mode aerosols on-line. The limitation of the DMA or SEMS for measurement of particles larger than 0.2 xm in diameter is the multiple charging that allows particles of two or more different sizes to contribute a given mobility fraction. Regardless of... 

With an ion production rate of 104 ions/(cms s) and an aerosol concentration of 5 x 104 particles/cm3, equilibrium would be achieved in about 2 s. For atmospheric aerosols where the ion production rate may be only 10 ions/(cm3 s), even though aerosol concentrations of 5 x 104 particles/cm3 are not uncommon, it takes approximately 1700 s (or about 30 min) for equilibrium to be achieved. O Connor and Sharkey (1960) report that equilibrium conditions usually prevail in air coming from the ocean. Over an industrial city, however, measurements indicated that the equilibrium charge distribution is not attained (Nolan and Doherty, 1950). This difference is attributed to the shorter time span between the production of the aerosol over the city and its measurement. 

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