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| - New Real-Time Technique toMeasure the Size Distribution ofWater-Insoluble Aerosols
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| - To date, there has been much research into the sizedistribution of ambient atmospheric aerosols, particularlyeither the total aerosol population or water-soluble ionicspecies such as sulfate or nitrate. Meanwhile, therehave been virtually no size-resolved measurements of water-insoluble aerosols (WIA). This has been due to a lack ofpractical measurement technology rather than a reflectionof the importance of WIA to climate and health. Particlesolubility influences the planetary radiation balance bothdirectly and indirectly: solubility influences both the amountof hygroscopic growth (and thus light scattering) thatoccurs as a function of relative humidity and the ability ofparticles to serve as cloud condensation nuclei (andthus the lifetime and albedo of clouds). Also, recent informationsuggests that WIA may be harmful to human health. Toaddress these concerns, a new real-time technique hasbeen developed to measure the size-resolved concentrationof WIA. This technique involves the entrainment ofparticles into a liquid stream and measurement of theWIA size distribution using a liquid optical particle counter.The time resolution of this instrumentation is approximately4 min (depending on flow rate) and is capable of sizingand counting insoluble particles with diameters of 0.25−2.0 μm at atmospheric concentrations as low as 0.1 cm-3.Laboratory characterization using polystyrene latexspheres shows agreement within ±5% of the liquid streamand air stream particle concentrations when adjustedfor flow rate. The instrumentation was field-tested at arural site on the edge of the metro-Atlanta urban area. Duringthis test, the WIA concentration averaged 5% of thetotal particle concentration between 0.25 and 2.0 μm butreached as high as 35%.
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