Measurement of trace metal composition in diesel engine particulate and its potential for determining oil consumption: ICPMS (inductively coupled plasma mass spectrometer) and ATOFMS (aerosol time of flight mass spectrometer) measurements

摘要

Current regulations stipulate acceptable levels of particulate emissions based on the mass collected on filters obtained by sampling in diluted exhaust. Although precise, this gives us only aggregated information. If in addition to the mass-based measurements, detailed chemical analysis of the particulate matter (PM) is performed, additional subtle information about the combustion process can be revealed. This paper reports the results of detailed chemical analysis of trace metal in the PM emitted from a single-cylinder, heavy-duty diesel engine. The trace metal concentrations are used as an indicator of oil consumption. Two techniques were used to make the trace metal concentration measurements. PM was captured on filters and trace metals were quantified with an Inductively Coupled Plasma Mass Spectrometer (ICPMS), and also an Aerosol Time- of-Flight Mass Spectrometer (ATOFMS) was used to perform particle size and composition measurements in real time. Particle size distributions were also measured using a Scanning Mobility Particle Sizer (SMPS). Aerosol Time-of-Flight Mass Spectrometers have been widely used to study atmospheric aerosols, but only limited ATOFMS measurements have been collected for internal combustion engine exhaust emissions. The instrument yields data of a single particle size and composition for a particle size range from 0.2 to 3 micrometers. Mass spectral composition analyses are completed at a rate of up to ～200 particles per minute. In this work we compare trace metals, elemental carbon (EC) and organic carbon (OC) concentrations from the ATOFMS with more traditional filter- based and particle size distribution data to assess the utility of using ATOFMS for real-time fundamental engine exhaust studies. The data presented covers the operating modes of California Air Resources Board (CARB 8 mode) emissions test. Dramatic changes in trace metals, EC and OC, and PM size with changes in the engine operating modes are evident from both filters and ATOFMS, which illustrates that the chemical and physical characteristics of the PM, especially trace metals, EC and OC concentrations, are highly dependant on the engine operating conditions. The results show chemical compositions of each particle and the contribution of the lubricating oil to the PM.