Morphological properties of atmospheric aerosol aggregates

Ultrafine particles (smaller than about 0.1 μm) are often emitted from combustion and other high-temperature processes in the form of fractal-like aggregates composed of solid nanoparticles. Results of a study of atmospheric aggregates are reported. Particles were collected on transmission electron microscope grids fitted on the last two stages of a single-jet eight-stage low-pressure impactor for periods of a few minutes. Photomicrographs of transmission electron microscope grids from the impactor stages were analyzed to obtain the fractal dimension (Df) and prefactor (A) for aggregates. Df increased from near 1 to above 2 as the number of primary particles making up the aggregates increased from 10 to 180. Total particle concentrations in size ranges roughly equivalent to the low-pressure impactor stages were measured with a mobility analyzer and condensation particle counter. In one set of measurements, the fraction of the particles present as aggregates was about 60% for particles with aerodynamic diameters between 50 and 75 nm and 34% for the range 75 to 120 nm. The total aggregate concentration in the 50- to 120-nm size range was about 400 ml−1. The primary particles that make up atmospheric aggregates are more polydisperse than soot aggregates generated from a single laboratory source, an ethane/oxygen flame. Most measurements were made in the Los Angeles area, where the aggregates may represent a signature for diesel emissions. Rural aggregate concentrations in the size range 50 to 120 nm were less than 1% of the concentrations at urban sites. The data will permit better estimates of atmospheric aggregate residence times, transport, and deposition in the lung, optical extinction, and heterogenous nucleation.

[1]  D. E. Rosner,et al.  Fractal-like Aggregates: Relation between Morphology and Physical Properties. , 2000, Journal of colloid and interface science.

[2]  D Mark,et al.  Characterization of Particles from a Current Technology Heavy-Duty Diesel Engine , 2000 .

[3]  S. Friedlander,et al.  Smoke, dust, and haze , 2000 .

[4]  Y. Kaufman,et al.  Effects of black carbon content, particle size, and mixing on light absorption by aerosols from biomass burning in Brazil , 1998 .

[5]  A. M. Brasil,et al.  a Recipe for Image Characterization of Fractal-Like Aggregates , 1998 .

[6]  Heinz Burtscher,et al.  High fractal-like dimension of diesel soot agglomerates , 1998 .

[7]  D. E. Rosner,et al.  Translation Brownian Diffusion Coefficient of Large (Multiparticle) Suspended Aggregates , 1995 .

[8]  S. Friedlander,et al.  Microstructure of Agglomerates of Nanometer Particles , 1995 .

[9]  S. Friedlander,et al.  Size distributions of polycyclic aromatic hydrocarbons and elemental carbon. 2. Ambient measurements and effects of atmospheric processes. , 1994, Environmental science & technology.

[10]  Ian Colbeck,et al.  The measurement of the fractal dimension of individual in situ soot agglomerates using a modified millikan cell technique , 1994 .

[11]  S. Friedlander,et al.  Note on the Power Law Equation for Fractal-like Aerosol Agglomerates , 1993 .

[12]  P. Buseck,et al.  Fractal geometry of carbonaceous aggregates from an urban aerosol , 1993 .

[13]  Hung V. Nguyen,et al.  The Mobility and Structure of Aerosol Agglomerates , 1993 .

[14]  S C Soderholm,et al.  Role of the alveolar macrophage in lung injury: studies with ultrafine particles. , 1992, Environmental health perspectives.

[15]  A. Weber Characterization of the geometrical properties of agglomerated aerosol particles , 1992 .

[16]  Themis Matsoukas,et al.  Dynamics of aerosol agglomerate formation , 1991 .

[17]  A. Hurd,et al.  Growth and Structure of Combustion Aerosols: Fumed Silica , 1990 .

[18]  B. H. Kaye A random walk through fractal dimensions , 1989 .

[19]  A. Schmidt-ott,et al.  New approaches to in situ characterization of ultrafine agglomerates , 1988 .

[20]  G. Mulholland,et al.  Cluster size distribution for free molecular agglomeration , 1988 .

[21]  James W. Gentry,et al.  Structural analysis of soot agglomerates , 1987 .

[22]  Constantine M. Megaridis,et al.  Morphology of flame-generated soot as determined by thermophoretic sampling , 1987 .

[23]  G. Cass,et al.  Characteristics of atmospheric organic and elemental carbon particle concentrations in Los Angeles. , 1986, Environmental science & technology.

[24]  L. Sander,et al.  Diffusion-limited aggregation, a kinetic critical phenomenon , 1981 .

[25]  J. Klett,et al.  Microphysics of Clouds and Precipitation , 1978, Nature.

[26]  T. Witten,et al.  Long-range correlations in smoke-particle aggregates , 1979 .

[27]  J. J. Collins,et al.  Design and evaluation of a new low-pressure impactor. 2 , 1979 .

[28]  Richard C. Flagan,et al.  Design and evaluation of new low-pressure impactor. I , 1978 .

[29]  Benjamin Y. H. Liu,et al.  On the performance of the electrical aerosol analyzer , 1975 .

[30]  Samuel Natelson,et al.  Aerosols and atmospheric chemistry: Edited by G. M. Hidy. Academic Press, New York, 1972. 348 pp. $14.50 , 1973 .