Condensation nuclei counts

Table I. Observed Condensation Nuclei Counts in Different Atmospheric Conditions, September Experiments, 1985...

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. 

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. 

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... 

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. 

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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