Design , Modeling , Optimization , and Experimental Tests of a Particle Beam Width Probe for the Aerodyne Aerosol

نویسندگان

  • J. Alex Huffman
  • John T. Jayne
  • Frank Drewnick
  • Allison C. Aiken
  • Timothy Onasch
  • Douglas R. Worsnop
  • Jose L. Jimenez
چکیده

Aerodynamic lens inlets have revolutionized aerosol mass spectrometry by allowing the introduction of a very narrow particle beam into a vacuum chamber for subsequent analysis. The real-time measurement of particle beam width after an aerodynamic lens is of interest for two reasons: (1) it allows a correction to be made to the measured particle concentration if the beam is so broad, due to poor focusing by non-spherical particles, that some particles miss the detection system; and (2) under constant lens pressure it can provide a surrogate particle non-sphericity measurement. For these reasons, a beam width probe (BWP) has been designed and implemented for the Aerodyne Aerosol Mass Spectrometer (AMS), although this approach is also applicable to other instruments that use aerodynamic lens inlets. The probe implemented here consists of a thin vertical wire that can be precisely positioned to partially block the particle beam at fixed horizontal locations in order to map out the width of the particle beam. A computer model was developed to optimize the BWP and interpret its experimental data. Model assumptions were found to be reasonably accurate for all laboratory-generated particle types to which the model was compared. Comparison of particle beam width data from a number of publications are also shown here. The model was then used to optimize the choice of the BWP dimensions, and to guide its use during continuous operation. A wire diameter approximately 1.55 times larger than the beam width to be measured provides near Page 2 of 55 4/10/2005 optimal sensitivity toward both collection efficiency and surrogate non-sphericity information. Wire diameters of 0.62 mm and 0.44 mm (for the AMS “long” and “short” chambers respectively) provide reasonable sensitivity over the expected range of particle beam widths, for both spherical and non-spherical particles. Three other alternative BWP geometries were also modeled and are discussed. 30 31 32 33 34 Page 3 of 55 4/10/2005

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Design, Modeling, Optimization, and Experimental Tests of a Particle Beam Width Probe for the Aerodyne Aerosol Mass Spectrometer

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تاریخ انتشار 2005