The ideal aerosol instrument determines the size, composition, and morphology of each particle sampled from a gas stream in real time (Friedlander, 1971; Flagan, 1993). Recently, instruments approaching this ideal have started to appear in a number of laboratories around the world. The first commercial instrument is now available as well (http://www.tsi.com). The instruments perform on-line single particle analysis (OSPA) because they analyze individual particles in real-time.
Since the advent of OSPA tools, there has been a burst of research activity to improve existing designs and develop new designs that complement the earlier ones. This issue presents recent results from 12 of the active research groups developing and deploying these instruments.
A significant issue in OSPA is efficient transmission of the particles from near atmospheric pressure to the microtorr pressures common in the chemical analysis stages. The first two papers are devoted to inlet design (Petrucchi et al., 2000; Mallina et al., 2000).
Although a few OSPA instrument designs have been deployed in laboratory and field applications for a number of years, there is still tremendous potential to apply new analytical techniques to OSPA. The next two papers are characterizations of current instruments -- one on elemental analysis using mass spectrometry techniques (Reents and Ge, 2000); the other on how the particle matrix influences spectra in an ion trap mass spectrometer (Reilly et al., 2000). The next four papers present new techniques for analyzing individual particles or small groups of particles in real time. The first two use techniques particularly suitable for analyzing organic compounds (Tobias et al., 2000; Cabalo et al., 2000). The third design is very portable and lightweight making it ideal for installation on small aircraft (Jayne et al., 2000). The last is the first to use spectroscopic techniques on individual particles to obtain elemental analysis (Hahn et al., 2000).
The last four papers discuss applications of OSPA to environmental particles. Mounting these tools on aircraft presents a whole suite of problems not present with ground-based instruments, such as weight, power consumption, and volume. The next two papers (Coggiola et al., 2000; Thomson et al., 2000) present instrument designs suitable for these more demanding platforms. The final two papers present results from field work and demonstrate the kinds of valuable analytical data that can be obtained out of the complex mix of particles often observed in the atmosphere (Liu et al., 2000; Trimborn et al., 2000).
OSPA is still in its infancy. There are numerous analytical techniques currently applied to bulk samples and many of these are suitable for analysis of samples small enough to encompass one or a small group of particles. We anticipate that OSPA will also provide a range of analytical methods in the near future with the advantage of real-time data collection. This issue demonstrates the progress that has been made with some of the early instruments and some of the promise yet to come with techniques just making their appearance.
Cabalo, J.; A. Zelenyuk, T. Bear, and R.E. Miller. Two-Color Laser Induced Evaporation Dynamics of Liquid Aerosols Probed by Time-of-Flight Mass Spectrometry.
Coggiola, M.J.; Z. Shi, and S.E. Young. Airborne Deployment of an Instrument for the Real-Time Analysis of Single Aerosol Particles.
Friedlander, SK. The characterization of aerosols distributed with respect to size and chemical composition. II. Classification and design of aerosol measuring devices. J. Aerosol Sci. 2:331-340, 1971.
Flagan, RC in "Measurement challenges in Atmospheric Chemistry," Newman L. ed.; ACS:Washington CD 1993.
Hahn, D.W.; and M.M. Lunden. Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy.
Jayne, J.T.; D.C. Leard, X. Zhang, P. Davidovits, K.A. Smith, C.E. Kolb, and D.R. Worsnop. Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles.
Liu, D-Y.; K.A. Prather, and S.V. Hering. Variations in Nitrate Containing Particles in Riverside, CA.
Mallina, R.V.; A.S. Wexler, K.P. Rhoads, and M.V. Johnston. High Speed Particle Beam Generation: A Dynamic Focusing Mechanism for Selecting Ultrafine Particles.
Petrucchi, G.A.; P.B. Farnsworth, P. Cavalli, and N. Omenetto. A Differentially Pumped Particle Inlet for Sampling of Atmospheric Aerosols into a Time-of-Flight Mass Spectrometer: Characterization and Initial Results.
Reents, W.D., Jr.; and Z. Ge. Simultaneous Elemental Composition and Size Distributions of Sub-Micron Particles in Real Time using Laser Atomization/Ionization Mass Spectrometry.
Reilly, P.T.A.; A.C. Lazar, R.A. Gieray, W.B. Whitten, and J.M. Ramsey. The Elucidation of Charge-Transfer-Induced Matrix Effects in Environmental Aerosols via Real-Time Aerosol Mass Spectral Analysis of Individual Airborne Particles.
Thomson, D.; M. Schein, and D. Murphy. Particle Analysis by Laser Mass Spectrometry WB-57F Instrument Overview.
Tobias, H.J.; P.M. Kooiman, K.S. Docherty, and P.J. Ziemann. Real-Time Chemical Analysis of Organic Aerosols using a Thermal Desorption Particle Beam Mass Spectrometer.
Trimborn, A.; K.-P. Minz, and B. Spengler. On-line Analysis of Atmospheric Particles with a Transportable Laser Mass Spectrometer.
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