Condensation particle counting

Ararwal, J.K. and G.J. Sem, Continuous Flow, Single-Particle-Counting Condensation Nuclei Counter, J. Aerosol Sci. 11 343-358 (1980). 

When the pump is turned off, the condensation nuclei count decreases by ventilation and plate-out to that observed before the sampling process. Thus, there must be a process during the sampling period that shifts the particle size to a size detectable by the CNC. The "pump effect" has further been found to be proportional to the S(>2 concentrations (Figure 6). It was not observed when... 

An acoustical particle counter for counting and sizing fog droplets has been evaluated by Singh and Reist.161 Fog droplets, mostly in the size range of 5-30 pm, were measured by the acoustical particle counter as well as an optical and an electron microscope for comparison. The mean droplet diameters estimated from the acoustical particle counter were in agreement with the microscope values. A Rich 100 condensation nuclei monitor was also operated simultaneously during the fog droplet counting to monitor condensation nuclei counts. 

Condensation nuclei counter growth in alcohol-saturated chamber optical particle counting 37... 

Tuch et. al. [231] ran a Mobile Aerosol Spectrometer (0.1 to 2.5 pm) and an Electrical Aerosol Spectrometer (0.5 to 10 pm) side by side for 6 weeks and found both to be reliable with almost identical results. Total number counts agreed with results from a Condensation Particle Counter. 

Depending on the goals, a variety of procedures can be used to facilitate particle detection. In condensation particle counters (also called condensation nucleus (CN) and Aitken nucleus counters), particles as small as 3 nm diameter are detected through size enhancement and optical detection. The particles are introduced into a chamber that contains a supersaturated vapor (water or n-butyl alcohol is commonly used). Condensation on the particles enlarges them typically to several micrometers so that they can be readily detected and counted as they pass through the chamber. 

Particle-counting methods count particles present in ambient air and do not require the subject to be exposed to any test aerosol. The most commonly used method is condensation nuclei counting (CNC) in which a vapour, usually isopropyl alcohol, is condensed onto particles to grow them to a size that can be seen and counted, by a laser and/or a light-scattering system. 

In a study of the impact of printers as emission sources of VOCs, ozone and particulate matter on indoor air quality, ultrahne particles have been measured using Scanning Mobihty Particle Spectrometer-Condensation Particle Counter (SMPS-CPC) (Kagia et al. 2007). SMPS distributes from 20 to 500 nm diameter particles and CPC counts ultrahne particles. 

Nanoparticle penetration has been measured with a wide range of filter media by using silver nanoparticles from 3 nm to 20 nm at three different face velocities in order to define nanoparticle filtration characteristics of commercial fibrous filter media. After size classification by using a nano-DMA, the particle counts were measured by an ultrafine condensation particle counter (UCPC) both upstream and downstream of the test filter in order to determine the nanoparticle penetration for each specific... 

The most commonly used instrument to measure ultrafine particles anploys CPC technology. The CPC condenses vapour onto the sampled particles in order to grow them to a detectable size range. This type of instrument is relatively portable and user friendly. The primary disadvantage of this instrument is its inability to discriminate particulate sizes above the detection limit, which ranges from 3 to lOOnm on commercially available units, giving a total particle count [18]. Figure 9.1 shows an example of a typical CPC used to characterize ultrafine particles. 

In an alternative to counting the number of condensed particles, one can try to monitor the concentration of remaining solute [44], or some other thermodynamic property that evolves with cluster formation for example, microcalorimetry can measure the heat absorbed as crystallization occurs, and thus can draw a de-supersaturation curve [45]. Needless to say, none of the above directly or indirectly touches upon the question of the internal structure of the generated clusters. 

The large amount of S in the particles suggested that S02 gas molecules or small sulfur-containing particles condense on to the surface of soil dusts during their transportation from China. Figure 4.22 illustrates an elemental map for Si distribution in coarse particles within a total scanning area of 25 pm x 25 pm. The scale bar shows the peak count of characteristic X-rays by pixel of the scan area. 

In this experiment, tritiated water is purified by simple distillation, and the tritium beta particles in the condensate are measured with a liquid scintillation (LS) counter. Such distillation also can collect tritiated water samples from solids. Tritium in other forms must be processed before it can be counted like tritium in water for example, tritiated hydrogen gas and tritiated organic substances can be oxidized to form water. Additional separations may be needed if the liquid or solid sample contains radioactive gases or volatile substances other than tritium that may be collected with the distilled tritiated water. Such radioactive impurities can be identified in the data output from the LS counter of an energy spectrum that differs from that of pure tritium, or of counts in energy regions where tritium counts are not found. 

The Master talked over his own researches with his students. The whole subject of the"reality of the electron was discussed. There were two Wilsons in his laboratory at the time. Suddenly he turned to C.T.R.—that was the way he addressed Charles Thomson Rees Wilson. This boy, too, had originally come from Owens College. Thomson had been watching him at work with his dust counter. Wilson had noticed that particles of dust acted as nuclei around which moisture condensed as tiny droplets of water when the air was suddenly cooled by expansion. These dust particles were too small to be photographed, but when they were surrounded by droplets of water they became easily visible and could be photographed. He thus devised an ingenious method of counting dust particles of the air. 

That dust counting had given Wilson some wonderful training. Perhaps an electrical particle would act in the same way as tiny dust specks. He tried the experiment, and after innumerable trials he triumphed. He saw through his powerful microscope water vapor condensing into tiny droplets around Thomson s negatively charged particles or electrons. 

Condensation nucleus (CN) concentration CN counter Expose particles to a high supersaturation, typically of butanol vapor particles grow to size where they can be optically detected and counted -b... 

By the compression of 1 gr. of saturated water vapour at 100° to saturated water vapour at 101°, we have an emission of 1-2 cal. If this heat is not allowed to escape, we do not obtain saturated water vapour at 101°, but superheated steam at a correspondingly higher temperature. Conversely, if we allow saturated water vapour to expand adiabatically, condensation takes place. We may mention that this spontaneous condensation of water vapour, which for a slight expansion takes place only in the presence of dust particles or ions, has been successfully employed in counting the number of ions or nuclei in the vapour. 

Many of the disperse systems which are commonly observed in nature or in the laboratory owe their origin, as we have seen, to the imbalanced forces which act at phase boundaries. Others, however, depend upon the existence of molecules so large that they must be deemed to count in a macroscopic sense as particles themselves. Such are the molecules of proteins like gelatine, polysaccharides like starch, and the poly condensation products formed in the laboratory from substances with several functional groups. 

Some common size range descriptions for atmospheric aerosol particles and droplets are shown in Tables 1.5 and 1.6. These ranges and descriptions are based mostly on the techniques used to determine the sizes [122,124,125]. Aitken particles and droplets (diameters less than 0.2 pm) are typically detected using an Aitken nucleus counter (also called a Nolan-Pollak counter or a Poliak counter). Here, the aerosol is introduced into a chamber containing vapour-saturated gas. Rapid volume expansion and adiabatic cooling are used to induce supersaturation in the gas, which in turn causes condensation on the original particles, which act as nuclei [122, 125]. This makes the original, small particles or droplets easy to observe and count with a microscope. (The principle just described is somewhat similar to the operation of a Wilson cloud chamber (see Section 7.1.4).)... 

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