10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Morphology and Comparisons of BC Mass Concentrations Measured by LII, CAPS, and PAX of PM Emitted from a Grand Cherokee and a Ford F-150 under Different Drive Cycles
FENGSHAN LIU, Fadi Araji, Greg Rideout, Prem Lobo, Gregory Smallwood, National Research Council Canada
Abstract Number: 537 Working Group: Instrumentation
Abstract Combustion-generated ultrafine particulates pose a serious concern for human health and climate warming. These nano-sized particles, when inhaled, are able to penetrate deep into the lungs and onto organs. Their black carbon (BC) component is strongly light-absorbing and has a strong climate warming effect. To establish a reliable BC inventories and evaluate BC mitigation techniques such as after-treatments and novel design of combustion devices or fuel technology, it is paramount to develop capabilities for real-time and accurate BC mass concentration measurements. BC aerosols contain different levels of elemental carbon (EC) and organic carbon (OC), depending on the combustion conditions and fuels. Various BC mass measurement instruments, which were developed based on a specific phenomenon of light and matter interactions, have been developed and extensively deployed for BC mass measurements. Unfortunately, there exists fairly large uncertainty in BC mass concentrations measured by various instruments, since they respond differently to variations in the physical (size, morphology, and the micro-structure) and chemical (EC/OC ratio) properties of the BC containing particles.
In this study, the BC mass concentrations of particulate matter (PM) emitted from two light duty trucks operated on a chassis dynamometer under different drive cycles were measured using a cavity-attenuated phase shift (CAPS) PMSSA monitor (at 660 nm), a photoacoustic extinctiometer (PAX) (at 870 nm), and an Artium LII 300 based on the laser-induced incandescence (LII) technique. The vehicles tested were a port fuel injection (PFI) Jeep Grand Cherokee and a gasoline direct injection (GDI) Ford F-150. During each test, the vehicle exhaust was directed into a Code of Federal Regulations compliant (CFR 1065) full-flow constant volume sampling system and diluted with high-efficiency particulate air (HEPA) filtered room air. The diluted exhaust was measured by CAPS and PAX, while the BC mass concentration measurement by LII300 was made in the undiluted exhaust directly from the vehicle tailpipe. The dilution ratio was evaluated by monitoring the CO2 concentrations. To help understand the potential differences in the mass concentrations measured by the different instruments, an ESPnano sampling device was also deployed to collect PM particles on 3-mm copper grids for TEM imaging and subsequent analysis for particle morphology.
The objective of this study is to understand the relative performance of the three tested real-time BC mass instruments applied to vehicle emissions under different drive cycles. The differences in the measured BC mass concentrations measured by CAPS, PAX, and LII are discussed in terms of the particle morphology, the level of concentration, and the drive cycle, which affects the combustion mode and hence the EC/OC ratio and carbon atom structure. In addition, the absorption coefficients measured by CAPS and PAX are used to infer the Ångström absorption exponent (AAE) of PM aerosols emitted from the two trucks at different drive cycles.