ABSTRACT. Composition and size of individual submicron particles have been measured us ing a laser atomization r r r r r ionization mass spectrometry technique, the Particle Blaster. Individual particles are quantitatively converted to atomic cations, providing information on both their complete elemental composition and particle size. Measured average atomic ratios for ; 100 nm particles of sodium chloride is ( ) ( ) 1.12 " 0.36 Cl:Na , for 50 nm particles of silica is 1.93 " 0.52 O:Si , and for 64 ( ) ( ) nm polystyrene latex spheres PSL is 1.13 " 0.19 H:C , in excellent agreement with the empirical formulae. Calculated particle sizes agree well with electrostatic classi er or TEM measurements in the size range of 17-900 nm diameter for particles of sodium chloride, silicon, and PSL. Size distributions are also obtainable, giving narrower distributions than are measured with an electrostatic classier, for particles of alumina, silica, sodium chloride, and PSL spheres. Comparison with TEM data shows comparable primary particle s izes, but numerous particle aggregates are detected by the Particle Blaster which are unreported by the TEM measurements.
Abstract. A number of laboratory experiments indicate that hydrophobic carbonaceous particles activate at lower supersaturations than is predicted by KOhler theory. Since a significant fraction of the global energy balance uncertainty is due to the so-called indirect effect, that of clouds, quantifying which particles activate is crucial to accurate prediction of climate. Most material surfaces obtain a fixed charge in water, and this is the case for many materials found in atmospheric aerosols. This fixed charge generates a charge double layer near the material surface which lowers the water activity. In the presence of this surface fixed charge, hydrophobic particles activate at low supersaturations. Since a small number of soluble ions in the particles causes them to only activate at higher supersaturations, surface charge activation is not relevant to activation of particles in the atmosphere. Thus laboratory experiments that measure the growth and activation of hydrophobic particles are measuring an effect, the surface charge effect, that is probably not relevant to the atmosphere.
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