Evaluation of Gravimetric Method to Measure Light-Duty Vehicle Particulate Matter Emissions at Levels below One Milligram per Mile (1 mg/mile)

The California Air Resources Board (CARB) adopted the Low Emission Vehicle (LEV) III regulations in January 2012, which lowered the particulate matter (PM) emissions standards for light-duty vehicles (LDVs) from 10 milligrams per mile (10 mg/mile) to 3 mg/mile beginning with model year (MY) 2017 and 1 mg/mile beginning with MY 2025. To confirm the ability to measure PM emissions below 1 mg/mile, a total of 23 LDVs (MY pre-2004 to 2009) were tested at CARB's Haagen-Smit Laboratory (HSL) (10 LDVs) and the United States Environmental Protection Agency's (US EPA) National Vehicle and Fuel Emissions Laboratory (NVEFL) (13 LDVs) using the federal test procedure (FTP) drive schedule. One LDV with PM emissions ranging from 0.6 - 0.8 mg/mile was tested at three CARB HSL test cells to investigate intra-lab and inter-lab variability. Reference, trip, and tunnel filter blanks were collected as part of routine quality control (QC) procedures. Reference and trip blanks showed the well-documented filter weighing and handling process had negligible impact on final test values. Tunnel blank data indicated the CARB HSL and US EPA test cells were equally clean, with a background PM level around 0.16 mg/mile. During this evaluation, all but three vehicles showed FTP weighted emissions under 1 mg/mile. Statistical analysis of the repeatability and reproducibility of the gravimetric method demonstrated that LDV test cells were able to distinguish vehicle PM emission levels below 1 mg/mile from the measurement system contribution. CARB's HSL intra-lab variability was greater than inter-lab variability.