Design and Development of a Field-Portable Tandem Raman and Elemental Aerosol Spectrometer (TREAS) for Near Real-time Aerosol Measurement
Nicholas Pugh, ORTHODOXIA ZERVAKI, Kabir Rishi, Pramod Kulkarni, Centers for Disease Control and Prevention, NIOSH
Abstract Number: 372
Working Group: Instrumentation and Methods
Abstract
We present design and development of a hand-portable, battery-operated Tandem Raman and Elemental Aerosol Spectrometer (TREAS) for the near real-time quantification of atomic and molecular speciation of workplace aerosols. The instrument uses an automated cyclical “collect-analyze-ablate” scheme, where aerosol is first sampled onto a rotating electrode as a dry spot sample, followed by its non-destructive molecular analysis using laser Raman Spectroscopy (RS). The dry spot sample is then ablated by a series of pulsed spark plasma discharges and the elemental quantification is obtained using spark emission spectroscopy (SES). The scheme allows time resolution of a few to several minutes. Laboratory experiments were conducted to evaluate the instrument’s time-resolution, limits of detection (LODs), uncertainty, and dynamic range for common workplace aerosols such as respirable crystalline silica (RCS) and titanium dioxide (TiO2). The mass LODs for RCS were approximately 306 (±14) ng, and 88 (±11) ng using RS and SES, respectively, while for TiO2, they were 10 (±0.4) ng, and 28 (±2) ng using RS and SES, respectively. These LODs were lower than those achieved by the standardized X-ray diffraction method (3-10 μg) for particulate samples. Ability of TREAS to speciate α-quartz and rutile TiO2, even in the presence of interferants like those found in fracking sand dust and aerosols generated during the grinding of engineered stone countertops, was assessed using laboratory test aerosols. The tandem molecular and atomic emission measurements in TREAS can allow both elemental identification and differentiation between different oxidation states, such as chromium (VI and III) in welding fumes. The ability of TREAS to measure in near-real time was demonstrated by continuously measuring transient aerosol concentrations. The study demonstrates the potential of TREAS to offer on-site, near real-time quantification with high specificity and sensitivity for many occupationally relevant aerosols.