Novel electrical mobility based instruments for real-time ultrafine aerosol measurements: Design, development, and testing

A new instrument, called the Miniature Electrical Aerosol Spectrometer (MEAS) has been designed for measurement of aerosol size distributions in near real time. The salient features of this instrument include its compact size, fast response, single-flow operation, potential passive operation, and a design that will enable eventual miniaturization. This thesis presents the MEAS design, development, testing, and extensions for other applications.;MEAS has a rectangular cross-section with two main regions: Electrostatic Precipitator (ESP) region and Classification region. The ESP section enables charged particle injection into the classification region where the particles are size-segregated based on electrical mobility. Particles are collected in the classifier region on a series of collection plates that are connected to electrometers. The combination of operating flow conditions, instrument design characteristics, and the detector signal strength are used with a data inversion routine to obtain particle size distributions in near real-time. A theoretical model for instrument flow and electric fields is obtained to enable optimization of collection characteristics as a function of various design parameters on real-time basis. The theoretical model is validated with computational fluid dynamics (CFD) calculations and an optimal instrument operation domain is identified. The accuracies and limitations of size distribution measurements with MEAS are discussed, accounting for transfer function, the sampled distribution, and detector characteristics.;The quality of MEAS size distribution measurements is dependent on the accuracy of inversion of the electrometer signals. An inversion routine based on regularization technique is developed to effectively calculate particle size distribution from a broad set of kernel functions and relatively noisy electrometer signals. The inversion routine solves a set of ill-posed Fredholm-type integral equations by optimizing the balance of smoothness and accuracy of the calculated aerosol size distribution. The regularization is achieved using L-curve optimization method combined with curvature minimization technique. The effect of electrometer noise and upstream particle concentrations on the accuracy of inversion is determined. Two MEAS prototypes were fabricated and the individual components of the instrument were tested. Aerosol size distribution measurements and comparison with commercial instruments such as Scanning Mobility Particle Sizer (SMPS, TSI Inc.) and Fast Mobility Particle Sizer (FMPS, TSI Inc.) in the laboratory and field (NYSDEC mobile testing lab) validate the theoretically calculated transfer functions and the effectiveness of the inversion algorithm. Second MEAS prototype was designed to reduce electrometer noise in order to enable fast and accurate measurements, and for extension to compositional analysis.;The distinct features involved with the MEAS design makes it suitable for other applications in the field of aerosol monitoring. For such applications, instruments were designed, developed, fabricated, and tested for aerosol compositional characterization [compositional MEAS (cMEAS)] and ultrafine particle counting [Miniature Ultrafine Particulate sensor (MUPS)]. With heated collection plates within cMEAS, size segregated organic carbon distribution can be obtained with this instrument. Temperature profile within the cMEAS was studied using FLUENT and the flow rate was optimized to avoid the aerosol vapor mixing inside the instrument. Experimental testing was performed to obtain the size segregated organic carbon distribution through Bobcat engine exhaust. The performance of the cMEAS was compared against Micro Orifice Uniform Deposition Impactor (MOUDI). For ultrafine measurement, the MUPS instrument was designed by optimizing the shape of the collection plate such that the electrometer signal from the collected particles is directly proportional to the total upstream ultrafine concentration. Preliminary experiments confirm that the MUPS can indeed provide a real-time measurement of ultrafine concentration. The development of MEAS, MUPS, and cMEAS provide a next-generation set of tools for ultrafine measurement.