10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Evaluation of an Improved CPMA-Electrometer Reference Mass System in Measuring Black Carbon Particles
JOEL CORBIN, Alireza Moallemi, Jason S. Olfert, Fengshan Liu, Kevin Thomson, Gregory Smallwood, Prem Lobo, National Research Council Canada
Abstract Number: 1420 Working Group: Instrumentation
Abstract For the calibration of instruments which measure the mass concentration of airborne particulate matter (PM), a traceable and sensitive reference system for mass concentration measurements is required. The CPMA-electrometer reference mass system (CERMS) satisfies these requirements, and has been demonstrated to perform reliably with low-volatility-organic as well as black-carbon aerosols, down to 5 µg m-3 concentrations (Dickau et al., 2015). This lower limit of detection (LOD) is satisfactory in the context of emissions testing, but only moderately so in the context of atmospheric pollution monitoring, where minimum of 1 µg m-3 is desirable.
The combined relative uncertainty of the CERMS has been previously reported as 4% (Dickau et al., 2015), but this relative value does not describe the LOD (an absolute value). Previous work has identified sources of uncertainty stemming from flow-meter imprecision, CPMA setpoint imprecision, CPMA setpoint bias, electrometer imprecision, and electrometer bias. Of these factors, the electrometer-bias uncertainty (resulting from baseline drift) is the only absolute value, and therefore becomes more important at lower concentrations; i.e., at the LOD. Here, we will systematically quantify and evaluate this uncertainty in terms of the Allan variance of the CERMS signal and corresponding baseline, for a system with an upgraded electrometer relative to the prior work. The utility of the upgraded CERMS will then be demonstrated using the calibration of an Artium LII 300 in High-Sensitivity mode, which is capable of detecting black carbon (BC) concentrations to levels of 0.2 µg m-3 and below.