HR: 10:45h
AN: A41G-02    [PDF]
TI: Evolution of Organic-Carbon/Black-Carbon Nanoparticle Size and Mixing State Near the Point of Emission
AU: * Jacobson, M Z
EM: jacobson@stanford.edu
AF: Dept. of Civil and Env. Engineering, Stanford University, Terman M-31, Stanford, CA 94305-4020 United States
AU: Seinfeld, J H
EM: seinfeld@caltech.edu
AF: Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: The regional and global radiative effects of fossil-fuel soot (black carbon plus organic matter) are predicted to depend substantially on its mixing state, and the mixing state begins to evolve at the point of emission. One set of field data (1) have shown that, within minutes of emission, the soot particle size distribution can evolve substantially, eliminating a 10-nm nucleation-mode peak, consisting mostly of organic matter, in favor of a larger peak around 40-50 nm, which may merge with the 70 nm emission peak of black carbon. Because the number of small particles in the data set decreased significantly while the number of large particles did not, it was hypothesized in that study that Brownian coagulation played a large role in the evolution of the nanoparticle size distribution. Here, it is found that Brownian coagulation, alone, is insufficiently fast to account for the observed rapid evolution of the size distribution. However, the enhancement of Brownian coagulation due to Van der Waal forces offset by viscous forces together with enhancement due to soot particle fractal geometry can account for a much greater share of the evolution. These processes were represented together with aerosol emissions, nucleation, condensation, dissolution, hydration, and chemistry among 10 aerosol size distributions and gas chemistry in a high-resolution three-dimensional numerical simulation examining the internal mixing of soot among multiple size distributions. Results suggest that coagulation is important, not only for rapidly mixing organic carbon/black carbon nanoparticles, but also for creating new distributions from the interactions of soot with background particles. (1) Zhu, Y., W. C. Hinds, S. Kim, and C. Sioutas, JAWMA, 52, 1032-1042, 2002.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0322 Constituent sources and sinks
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting