Project at a Glance
Project Status: complete
Title: Very low PM measurements for light-duty vehicles (E-99)
Principal Investigator / Author(s): Jung, Heejung
Contractor: UC Riverside
Contract Number: 12-320
Research Program Area: Emissions Monitoring & Control
Topic Areas: Mobile Sources & Fuels
Present motor vehicle particulate matter (PM) emissions measurement regulations (Code of Federal Regulations [CFR] 40 Parts 1065 and 1066) require gravimetric determination of PM collected onto filter media from diluted exhaust. There have been discussions about whether current sampling and measurement practices are sufficiently accurate in quantifying PM at the proposed 3 mg/mi standards, and even more so at the 1 mg/mi PM emissions standards for LEV III light-duty vehicles.
The objective of this research program is to examine modifications to gravimetric PM measurement that preserve the integrity of the method and increase the robustness of the PM measurements, while decreasing the testing variability. For this program, a Lower PM Source vehicle with an emissions rate of < 1 mg/mi and a Higher PM Source with an emission rate just below 2 mg/mi were evaluated over a series of tests designed to characterize PM mass emissions for 3-bag Federal Test Procedure (FTP) tests, 4-bag FTP tests, and the US06 test. The tests evaluated cumulative vs. individual bag filter PM collection, different sampling flow rates/filter face velocities (FFVs), and changes in dilution factor (DF) with a partial flow sampling system (PFSS).
Comparisons between different methods did not show statistically significant differences in the PM mass emission rates for most of the conditions, i.e., increased FFV, reduced DF, or combining/cumulative filters. However, it was found that greater mass could be collected on the filter over the course of testing, increasing the signal-to-noise ratio of the method. Additionally it was estimated that the measurement uncertainty (based on a propagation of error analyses) could be reduced by a factor of four between the traditional one filter per phase, FFV=100 and a DF=7, in comparison to a composite 4-bag FTP test, FFV=150 and a DF=5.
The E-99 project revealed several confounding influences for the quantification of PM emissions from vehicles that invite further investigation. These include understanding test-to-test variability, which can exceed 100% (0.1 to 0.5 mg/mi for the Lower PM Source and 1.2 to 2.0 mg/mi for the Higher PM Source) between tests conducted over a 12 month time period, PFSS to CVS comparison where 5-10% absolute bias was reported, characterizing the PFSS dilution factor to identify possibly sources of bias between the CVS and the PFSS, and understanding sample contamination between tests where excessive exhaust temperatures may contribute to PM emissions variability.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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