Aitken concentration distribution

Novakov and Penner (1993) measured the mass size distributions of sulfur, organic carbon, and chlorine (characteristic of sea salt) as well as the CCN concentration (at 0.5% supersaturation), nss, and Aitken nuclei concentrations at a mountain peak in Puerto Rico. 

Particle Number Concentration and Size Distribution. The development of aerosol science to its present state has been directly tied to the available instrumentation. The introduction of the Aitken condensation nuclei counter in the late 1800s marks the beginning of aerosol science by the ability to measure number concentrations (4). Theoretical descriptions of the change in the number concentration by coagulation quickly followed. Particle size distribution measurements became possible when the cascade impactor was developed, and its development allowed the validation of predictions that could not previously be tested. The cascade impactor was originally introduced by May (5, 6), and a wide variety of impactors have since been used. Operated at atmospheric pressure and with jets fabricated by conventional machining, most impactors can only classify particles larger... 

The particle number size distributions and concentration levels measured at the Central European stations were remarkably similar. The median particle number size distributions did not change significantly from season to season, and the differences between the stations were not very large (N50 from 2,500 to 3,100 cm-3). The variability of nucleation and small Aitken particles was elevated... 

Figure 9 (adapted from [18]) shows some of the typical correlations between particle number concentrations between 30 and 100 nm (here referred to as Aitken mode, although a more rigorous derivation would require actual modal fitting) and concentrations between 100 and 500 nm ( accumulation mode ). The idea of this kind of plot is to show the possible correlation between the two aerosol modes, to indentify some of the main particle number size distribution types, and whether the particle number concentrations in both modes increase in the same rate. 

Fig. 7-5. Coagulation behavior of particles produced by nucleation. [Adapted from Walter (1973).] A continuous generation of embryos with 1.2x 10 3 pm radius is assumed. Left Variation of the distribution function with time in the absence of preexisting particles production rate q = 106 cm" s"1. Right Steady-state distributions for different concentrations of preexisting large particles (r > 0.1 pm) production rate q = 102 cm 3 s-1 number density of preexisting large particles N0 = 270/3. The dashed curve (for /3 = 1) is obtained from the steady-state distribution 12 h after terminating the source of embryos. The apparent lifetime of Aitken particles for coagulation is here greater than that indicated in Fig. 7-4 because of the smaller number density of particles.

In the absence of significant transport of continental aerosols, particles over the remote oceans are largely of marine origin (Savoie and Prospero 1989). Marine atmospheric particle concentrations are normally in the range of 100-300 cm-3. Their size distribution is usually characterized by three modes (Figure 8.15) the Aitken (Dp < 0.1 pm) the... 

Very early on, Aitken (1923) showed that most particles in the atmosphere are smaller than 0.1 pm diameter and that their concentrations vary from some hundreds per cm over the ocean to millions per cm in urban areas. Junge (1955,1963,1972) measured the atmospheric aerosol number size distribution and concentration in urban and non-urban areas as functions of altitude and site. He established the standard form for plotting size distribution data log of AN/ADp versus logD, where N = number and Dp = particle diameter. He observed that this plot was a straight line that could be described by the equation AN/ADp = AD, where A and k were constants. He also noted that in the range from 0.1 to 10.0 pm particle diameter, k was approximately equal to 4.0. This distribution mode was widely known as the Junge distribution or the power law distribution. 

The nuclei or Aitken nuclei mode accounts for most of the Aitken nuclei count and originates primarily from the condensation and coagulation of highly supersaturated vapours. There is evidence that a prominent nuclei mode in the size distribution indicates the presence of substantial amounts of fresh aerosol. Many particles in the nuclei mode raise the Aitken nuclei. Usually, they do not greatly increase the aerosol mass concentration because the nuclei mode rarely accounts for more than a few percent of the total mass. 

Parameters of the activity size distribution of the aerosol-attached short-Uved radon decay products in air at different locations. Activity median aerodynamic diameter, AMAD, noted as AMD geometric standard deviation, Og fraction of the mode, fpi. The indices i = n, a and c represent the nucleation (Aitken nuclei), accumulation and coarse particles modes, Z = aerosol particle concentrations... 

In polluted regions, the number concentrations often exceed 10,000 cm and the Aitken and accumulation mode are shifted toward larger sizes (43). The size distribution shown in Figure 5 is an average of 192 size distributions obtained during a field eampaign in the highly polluted Po Valley, Italy, November 17, 1994,00.00-24.00 hr. The distribution consists of a nucleation and an accumulation mode. However, the nucleation mode occurred only occasionally. 

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