Portable Emission Measurement Systems (PEMS) are increasingly being used in a variety of transportation research projects to determine real-world vehicle emissions impacts. One of the key questions that remain is how wellthese systems perform compared to testing that occurs in controlled laboratory conditions. To help answer this question, three PEMS were carefully evaluated for both gasoline and diesel light-duty vehicles in a dynamometer test facility. The evaluation was focused on their accuracy, time-correspondence, and suitability to measure transient emissions. Both cumulative mass emissions and modal emissions for carbon monoxide(CO), hydrocarbons (HC), oxides of nitrogen (NOX), and carbon dioxide (CO2) were measured for three gasoline and three diesel vehicles on three widely varying driving cycles. All of the PEMS systems(including emissions analyzer and flow meters) proved to be both reasonably accurate and precise. The CO2 emissions measured by the PEMS were in excellent agreement(within 98%) with the measurements from the laboratory system. Other pollutants measured were found tobe in reasonable agreement(within 20% or better) for NOX and HC on dieselvehicles and CO on gasoline vehicles. Second-by-second emission rate measured using the PEMS matched well with the corresponding laboratory modal analyzer data on CO2, NOX and CO under all driving cycles. Transient emissions of all pollutants agreed within 10% of the two systems with more than 6000 data points compared from each vehicle. The results suggest that whenproperly set up, PEMS are capable of measuring emissions from both gasoline and diesel vehicles to an accuracy approaching that of conventional laboratory modal analyzer systems.
Abstract