Size segregation

Size-segregated particles (more than two stages)... 

To account for inhomogeneity in bubble sizes, d in Eq. (20-52) should be taken as / Ln,dffLn,d, and evaluated at the top of the vertical column if coalescence is significant in the rising foam. Note that this average d for overflow differs from that employed earlier for S. Also, see Bubble Sizes regarding the correction for planar statistical sampling bias and the presence of size segregation at a wall. 

A practical ramification of this rule is utilized in segregation studies. The most obvious way to study segregation by NMR/MRI is to use two different types of beads, one that is NMR-visible and the other not. However, size segregation studies can be performed by simply using two different sizes of NMR-visible particles because they have different overall spin densities, for the reason stated above. Therefore, the image intensity will depend on the relative concentration of each particle in a voxel. 

When considering the impact of uptake by aerosol, the chemical composition of the aerosol is also likely to be significant. Bates et al. (1998, 2001) measured strong variations in the chemical composition of the Aitken, accommodation and sea-salt dominated coarse modes that would influence the free radical uptake rates, particularly the extent of aerosol acidification. Without data on the size segregated aerosol chemical composition during SOAPEX-2 and the relevant laboratory data, it is not possible to calculate accurate accommodation coefficients. 

Better collection methods are needed for stack measurements. Virtual Impactors or other devices that avoid the bounce-off problems of cascade Impactors should be developed. Methods for collection of very large amounts of size-segregated particles suitable for detailed organic analyses are needed. Better low-blank filter and collection-surface materials that can withstand high stack temperatures are needed. Careful attention should be given to the determination of vapor-phase species of volatile elements and compounds. 

Comparisons Between Size-Segregated Resuspended Soil Samples and Ambient Aerosols in the Western United States... 

Horvath, H., Size Segregated Light Absorption Coefficient of the Atmospheric Aerosol, Atmos. Environ., 29, 875-883 (1995). 

Dibenzo[a,/]pyrene, a potent mutagen in the MCL-5 assay, was not detected in this analysis of SRM 1649. However, this 6-ring PAH XXIX was identified (but not quantified) by comparison to an authentic standard by Allen and co-workers (1998) in their analysis of size-segregated aerosols in urban Boston ambient air. Furthermore, in their August 1994 study of biologically active, particle-associated PAHs in ambient Riverside, California, Atkinson and Arey (1997) measured concentrations of 18, 20, and 15 pg m-3 of this compound for one daytime and two nighttime sampling events, respectively. These concentrations were 40-50% of the BaP concentrations in the same aerosol samples. 

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-... 

Allen, J. O., N. M. Dookeran, K. A. Smith, A. F. Sarofim, K. Taghizadeh, A. L. Lafieur, Measurement of Polycyclic Aromatic Hydrocarbons Associated with Size-Segregated Atmospheric Aerosols in Massachusetts, Environ. Sci. Technol., 30, 1023-1031 (1996). 

The coals were crushed to —20 mesh but were not further size segregated to avoid selective separation of the petrographic constituents of the coal. Analytical reagent grade methanol was obtained from Fisher Scientific Co. and used without further purification. It was stored over anhydrous calcium sulfate and degassed by intermittent evacuation of the storage flask. Reagent... 

Compositional Analysis of Size-Segregated Aerosol Samples... 

Cahill Wakabayashi Analysis of Size-Segregated. Aerosol Samples 215... 

With increased sensitivity, the size-segregating samplers have produced data that are most helpful in characterizing the size and composition of aerosols. The data from these samplers have been used to resolve a bimodal, and sometimes a trimodal, distribution of particles. 

Compositional analyses of size-segregated particles from ambient atmospheric aerosols are vital for understanding the sources and effects of these aerosols. Three challenges exist for analytical chemistry in the next decade ... 

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