Monitoring and Diagnostic Tools for Aerosol Beams from Different Aerodynamic Lenses

DONGWOOK KIM, Pedro Campuzano-Jost, Hongyu Guo, Leah Williams, Philip Croteau, John Jayne, Douglas Worsnop, Jose-Luis Jimenez, University of Colorado, Boulder

     Abstract Number: 437
     Working Group: Instrumentation and Methods

Abstract
An aerodynamic lens (ADL) (Liu et al., AS&T, 1995) consists of multiple constrictions in series and is used to collimate aerosol into a narrow beam, enabling its efficient transmission into an aerosol detection region while greatly reducing the gas-phase background. ADLs are widely used as inlets in real-time aerosol measurements with mass spectrometry. Depending on the design, an ADL transmits different size ranges of aerosols and focuses them differently. The aerosol transmission efficiency of an instrument with an ADL inlet can be affected by the focusing/pointing characteristics of an ADL. Here we introduce techniques to monitor the beam center positions and beam widths of an aerosol beam as a function of vacuum aerodynamic diameter using an Aerodyne aerosol mass spectrometer (AMS) and customized 2D beam width probe. Based on the information obtained from the beam measurements, we estimate the aerosol transmission efficiency using a simple aerosol beam dispersion model. Model results were consistent with measured aerosol transmission efficiency and particle deposition pattern images. These tools can be used to characterize different ADLs, estimate and optimize the particle transmission efficiency of an AMS, and monitor the stability of the focusing performance over time. We will present an example of inlet diagnostics using those tools and optimization of lens alignment to maximize particle transmission efficiency.