Alternatives to the Gravimetric Method for Quantification of Light Duty Vehicles Particulate Emissions
Measurement of particulate matter (PM) emission of light-duty vehicles (LDVs) is a complex issue with many stakeholders, including engine manufacturers, health effect scientists, climatologists and regulatory agencies. With particulate emission regulatory limits in California and United States decreased by more than two orders of magnitude since the 80s, efforts continue to investigate alternatives to the gravimetric method for quantification of LDVs PM emission.
Several alternative metrics including total particle number (TPN), solid particle number (SPN), black carbon (BC), and particle surface (PS) area were measured along with gravimetric PM mass to study the correlation between different methods, using a variety of LDVs chosen to represent different emission levels and a range of current technologies in the modern fleet. It was found that gravimetric PM mass is strongly dependent on chemical nature of the PM. Thus correlations of gravimetrically determined PM mass with alternative metrics were different between two different testing cycles (e.g. FTP vs SFPT-US06). Alternative metrics are free from such cycle dependency which is due to adsorption artifact and therefore considered as a good future metric or supplemental metric such as SPN for EU regulation. Particle surface (PS) area turned out to be very sensitive with wide range and current instrumentation has a room to improve in terms of measuring tunnel blank and reducing electrometer drift.