Design and fabrication of an electrostatic precipitator for infrared spectroscopy

Infrared (IR) spectroscopy is a direct measurement technique for chemical characterization of aerosols that can be applied without solvent extraction thermal treatment a priori. This technique has been used for chemical speciation, source apportionment, and detailed characterization of the complex organic fraction of atmospheric particles. Currently, most IR analyses are performed by transmission through porous membranes on which the particles are collected via filtration. The membrane materials interfere with the IR spectra through scattering and absorption that not only make extracting the chemical information on aerosol harder but also limit the lower extent of detection. An alternative IR measurement method that does not inherit such limitations is to collect the particles on an IR transparent material. We present an electrostatic precipitator (ESP) design that enables such measurements by collection on a zinc selenide (ZnSe) crystal. Through numerical simulations and rapid prototyping with 3D printing, we design and fabricate a device which is tested with polydispersed ammonium sulfate particles to evaluate the quantitative chemical composition estimates against particle count reference. Furthermore, with an image analysis procedure and using variable aperture of the IR spectrometer, we analyze the radial mass distribution. The collector has high collection efficiency (82 +/- 8 %) and linear response to mass loading (R-2 > 0.94) with a semi-uniform deposition. The method of design and fabrication is transferable to other applications, and the current ESP collector can provide directions for further design improvements.