Ultrafine aerosol particles size distribution

In a similar study, Allen and co-workers (1996) determined the particle size distribution for 15 PAHs with molecular weights ranging from 178 (e.g., phenan-threne) to 300 (coronene) and associated with urban aerosols in Boston, Massachusetts. As for BaP in the winter (Venkataraman and Friedlander, 1994b), PAHs with MW >228 were primarily present in the fine aerosol fraction (Dp < 2 /Am). A study of 6-ring, MW 302 PAH at the same site showed bimodal distributions, with most of the mass in the 0.3- to 1.0-/zm particle size size range a smaller fraction was in the ultrafine mode particles (0.09-0.14 /xm) (Allen et al., 1998). For PAHs with MW 178—202, the compounds were approximately evenly distributed between the fine and coarse (D > 2 /am) fractions. Polycyclic aromatic hydrocarbons in size-segregated aerosols col-... 

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It has been found that the "unattached" fraction is an ultrafine particle aerosol with a size range of 0.5 to 3 nm. In order to initiate studies on the formation mechanism for these ultrafine particles, a series of experiments were made in the U.S. Bureau of Mines radon chamber. By introducing SO into the chamber, particles were produced with an ultrafine size distribution. It has been found that the particle formation mechanism is supressed by the presence of radical scavengers. These experiments suggest that radiolysis following the decay of Rn-222 gives rise to the observed aerosol and the properties of the resulting aerosol are dependent on the nature and the amount of reactive gas present. 

FIGURE 9.7 Schematic of an atmospheric aerosol size distribution showing four modes. The original hypothesis of Whitby and co-workers is shown by the solid, trimodal curves, and the fourth, ultrafine particle mode, as well as the two peaks sometimes observed in the accumulation mode are shown by the dashed lines (adapted from Whitby and Sverdrup, 1980). 

In the past half-decade, extensive studies have focused on aerosol nucleation in aircraft exhaust plumes [79]. This interest has brought attention to the formation of volatile aerosols that might eventually evolve into cloud condensation nuclei [80], Measurements of ultrafine particles reveal remarkably high abundances in jet wakes at very early times (within 1 second of emission) (e.g., [81]). As in the background atmosphere, the classical homogeneous nucleation theory has been applied to explain the number and size distribution of these volatile microscopic particles [82,83], However, while achieving some initial success, the theory has not been able to explain more recent, detailed observations. 

Birmili W, Weinhold K, Nordmann S et al (2009) Atmospheric aerosol measurements in the German ultrafine aerosol network (GUAN). Part 1. Soot and particle number size distributions. Gefahrst Reinhalt Luft 69 137-145... 

Keywords Aerosol number and size distributions, Engineered nanoparticles, European environment, Exposure-response doses, Ultrafine particles... 

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Zhu Y, Hinds W, Kim S et al (2002a) Concentration and size distribution of ultrafine particles near a major highway. J Air Waste Manag Assoc 52 1032-1042 Zhu Y, Hinds W, Kim S et al (2002b) Study of Ultrafine particles near a major highway with heavy-duty diesel traffic. Atmos Environ 36 4323-4335 Zhu Y, Hinds W, Krudysz M et al (2005) Penetration of freeway ultrafine particles into indoor environments. J Aerosol Sd 36 303-322... 

Atmospherie aerosol particles are principally divided into fine and coarse partieles. The fine-particle-size range covers geometric particle diameters (Dp) 1 >Dp > 1000 nm. Particles with Dp > 1 pm are called coarse partiele. Fine particles are also defined as Dap > 2.5 pm (e.g., by inhalation toxieologists for which Dap is defined as the aerodynamic particle diameter). The entire number-size distribution can be principally described by four different aerosol particle modes (Table 2). Fine particles belong to the nucleation (ultrafine), the Aitken, or the accumulation mode (1). The fourth mode is the coarse particle mode. 

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