Determination of PEMS Measurement Allowances for Gaseous Emissions Regulated Under the Heavy-Duty Diesel Engine In-Use Testing Program: Part 1 – Project Overview and PEMS Evaluation Procedures

Under the U.S. Environmental Protection Agency's (EPA's) Heavy-Duty In-Use Testing (HDIUT) program, emission of non-methane hydrocarbons (NMHC), carbon monoxide (CO), and oxides of nitrogen (NO_x) have been regulated using Portable Emissions Measurement Systems (PEMS) during in-use field operation for heavy-duty on-highway diesel engines with 2007 or later model year designations. As directed by the EPA, the Engine Manufacturers Association (EMA), and the California Air Resources Board (CARB), additive emission measurement accuracy margins (measurement allowances) were experimentally determined for HDIUT to account for the measurement differences between laboratory testing with laboratory grade equipment and in-use testing with PEMS.

As part of a three-paper series, this paper summarizes the HDIUT measurement allowance program while focusing on the laboratory evaluations of the Sensors Inc. SEMTECH-DS PEMS. The objective of the project was to quantify PEMS measurement errors as compared to concurrent measurements from a 40 CFR Part 1065 compliant dynamometer test cell. PEMS measurement errors were also evaluated when subjected to various environmental disturbances. The error data recorded during laboratory testing were used to populate a Monte Carlo statistical model. The model was iterated to randomly combine the various sources of PEMS measurement errors, the results of which were used to determine the additive measurement allowances for in-use testing. Model validation exercises were conducted by comparing PEMS emission results with the Center for Environmental Research & Technology (CE-CERT) Mobile Emissions Laboratory during on-road testing.