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CPMA-Electrometer Reference Mass Standard (CERMS): A Traceable Calibration Method for Aerosol Mass Concentration Instruments
GREGORY SMALLWOOD, Joel Corbin, Jason S. Olfert, Prem Lobo, National Research Council Canada
Abstract Number: 96
Working Group: Aerosol Standards
Abstract
The mass concentration of aerosols is determined by a wide range of instruments employing a number of different measurement principles. The most significant gap in the calibration of these instruments is the lack of traceability. This limitation is avoided by using the centrifugal particle mass analyser (CPMA)–electrometer reference mass standard (CERMS) technique. All aspects of the CERMS technique are traceable to the SI, resulting in a traceable mass standard similar in principle to the calibration for CPCs. The CERMS is capable of classifying and measuring in-situ reference mass concentrations down to levels below 1 μg/m3 and in real-time (~1 Hz). Additional advantages of the CERMS are its low uncertainty (~3 %) and its measurement of a well-defined quantity: total post-CPMA suspended PM mass. The CPMA in the CERMS system classifies all particles by mass-to charge ratio, independent of particle properties, including morphology and composition. Depending on the principles of the measurement instrument undergoing calibration, it may be important to select particles with similar properties to what the instrument is designed to measure. For instance, when presented with a nonvolatile black carbon (BC) aerosol for calibration, CERMS may be used to calibrate instruments for the measurement of BC mass concentration.
The presentation discusses the validation and characterization of the CERMS technique from a metrological perspective. We will also summarize recent applications of the CERMS, including the demonstration of a size-specific BC mass absorption cross section and the characterization of the lower limits of detection of the LII 300 and PAX. The results demonstrate the linearity of the CERMS system, and that it is independent of the CPMA setpoint. The sensitivity of the CERMS is shown by characterizing the limits of detection of the LII 300 and PAX instruments. The results support the use of CERMS with appropriate sources for the calibration of instruments measuring aerosol mass concentrations.