AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Assessment of Measurement Methods using CAPS PMssa, PAX, Aethalometer, LII, and TOA for Measuring the Mass Concentration of Black Carbon Produced from a MiniCAST Soot Generator over a Wide Range of Setpoints
PREM LOBO, Fengshan Liu, Meghdad Saffaripour, Kevin Thomson, Gregory Smallwood, National Research Council Canada
Abstract Number: 214 Working Group: Instrumentation and Methods
Abstract Black carbon (BC) has been identified as a significant climate forcer just after CO2. Mitigation of BC emissions will provide benefits to the climate on a fairly short timescale due to the short lifetime of BC. To monitor BC mass concentrations, it is desirable to have real-time measurement capability, which is currently offered by a number of optically based measurement methods. Unfortunately, these methods are typically limited to providing optical properties and the conversion from them to aerosol mass concentration requires an empirical factor, which varies with the source of the aerosols but has been treated as a constant.
To understand how changes in black carbon particle properties affect the mass concentration measurements reported by different optically based instruments, extensive measurements of black carbon generated from a MiniCAST soot generator over a wide range of setpoints were conducted. The instruments were cavity attenuated phase shift with single scattering albedo (CAPS PMssa) particulate matter monitor (operated at 660 nm), photoacoustic extinctiometer (PAX) (operated at 870 nm), photoacoustic soot spectrometer, three wavelength (PASS-3) (operated at 405, 532, and 781 nm), laser-induced incandescence (LII 300), and a 7-wavelength aethalometer (between 370 and 950 nm). In addition, filter samples of black carbon particles were also collected for thermal optical analysis (TOA) to obtain the EC and OC contents and to provide benchmark mass concentrations for assessment of the optical methods, for Raman spectroscopy analysis of BC particle microstructure, and for transmission electron microscope (TEM) analysis for particle morphology.
The preliminary results indicate that there is reasonable agreement between the mass concentration measurements reported by LII, PAX, CAPS, and the aethalometer at most of the MiniCAST setpoints. However, PASS-3 measured lower aerosol absorption coefficients than CAPS and PAX (after conversion to the same wavelength for direct comparison). The filter samples are anticipated to provide further insight to the relationships between the optical properties measured by the different types of instruments. The results obtained in this study will help to improve our understanding of the relationship between the mass concentration measurement uncertainties of different optical instruments and the black carbon properties.