Aitken nuclei mode

Washout by rain greatly reduces the Aitken nuclei mode and the coarse particle mode but has little effect on the accumulation mode in the trimodal size distribution (Whitby, 1975). The origin of each mode of atmospheric aerosol size distribution can be associated with various aerosol formation mechanisms, such as Brownian motion of the particles smaller than 0.1 pm in diameter, which causes the particles to diffuse and by collisions to coagulate to larger sizes. Coagulation generates multimodal distributions and affects the shape and the chemical composition of the particles. 

The aerodynamic size distribution of radionuclide-associated aerosol particles is, as mentioned in Section 2, a surface distribution, and so it is trimodal, the first mode being the so-called Aitken nuclei mode, the second the accumulation mode and the third the coarse particle mode. Analytically, these modes can be summarised as follows ... 

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. 

E). The data rather indicate that the activity median aerodynamic diameter, AMAD, of Be-aerosols increases with increasing latitude (latitudinal effect). As cosmic radiation increases with latitude, the numbers of Be atoms and ions formed also increase with latitude and so there are more Be atoms and ions available either to form small aerosol particles in the nucleation (Aitken nuclei) mode and then growing or to be attached directly to the existing large particles in the accumulation and in the coarse particle modes thereby increasing the AMAD of the Be-aerosols. 

Figure 4.1 shows the mass aerodynamic size distribution of sulfate aerosols obtained by a low-pressure cascade impactor (LPI) (Bondietti and Papastefanou, 1993). In Figure 4.1 a is the frequency distribution of sulfate aerosols, in which are indicated the Aitken nuclei mode (I), the accumulation mode (II) and the coarse mode (HI), while in Figure 4.1b is the log-normal distribution of sulfate aerosols. This distribution was selected from 12 measurements made... 

Aitken nuclei mode 5-7, 13, 59, 80-82, 96, 97 alpha-recoil 32,35 aluminium-26 11, 12... 

---