Aerosol Raman Spectrometer for Near Real-time Measurement of Aerosols with High Specificity in Workplace Atmospheres

Surendra Devarakonda, Orthodoxia Zervaki, PRAMOD KULKARNI, Centers for Disease Control and Prevention, NIOSH

     Abstract Number: 621
     Working Group: Instrumentation and Methods

Abstract
We describe design and development of a hand-portable, battery-operated Aerosol Raman Spectrometer for near real-time measurement of chemical components of occupational aerosols. The prototype instrument employs, an automated cyclical “collect-analyze-ablate” scheme, where airborne particles are first sampled and collected on an electrode as a small deposit, following analysis for target analyte using Raman spectroscopy, and are subsequently ablated to collect the next batch of particulate sample. The semi-continuous scheme offers unattended and automated sampling and quantification of aerosol chemical component using Raman spectroscopy. Laboratory experiments were conducted to characterize time-resolution, detection limits, uncertainty, and dynamic range of measurement for various occupational aerosols of interest, such as respirable crystalline silica (RCS), titanium dioxide (TiO2), particulate Cr (VI), diesel particulate matter (DPM), graphene, and single-walled carbon nanotubes (SWCNTs). The detection limits for respirable crystalline silica (RCS) and TiO2 were found to be approximately 200 ng and 27 ng, respectively, which is approximately 2 to 3 orders of magnitude lower than those of the standard methods using the same aerosol sample collection time. The high specificity of the method was also demonstrated by distinguishing two polymorphs of TiO2, rutile and anatase, in a mixed aerosol. Ability to measure in near-real time was demonstrated by continuously measuring transient aerosol concentrations. The method was also successfully extended to measure crystalline silica content of aerosol samples obtained from hydraulic fracturing workplace that had relatively complex particulate matrix. While sample fluorescence can limit the applicability to a wide range of aerosol types, the study does demonstrate the potential of this hand-portable instrument to provide on-site near real-time quantification with high specificity and sensitivity for occupationally relevant aerosols.