On-Road NOx Emissions Evaluation of the Repair Effectiveness for Recalled Volkswagen Group Light-Duty Diesel Vehicles in the United States.

The admission by the Volkswagen Group in the fall of 2015 that they had duped the United States new vehicle emissions certification testing resulted in perhaps the most expensive violation of U.S. environmental vehicle emission regulations in its history. As part of the subsequent recall of more than 500 000 vehicles in the U.S., owners could sell their vehicles back to the companies or have them repaired. We have used a number of large on-road emission measurement data sets that were routinely collected before and after the recall to evaluate the fuel specific NOx emissions benefit for the vehicles that were repaired and remained in service. We found that on-road fuel specific NOx emissions were reduced by 83% from the prerepair group. The reductions increased to 91% if we only compare with vehicles that were fully repaired. NO2 emissions were dramatically reduced by an even larger percentage >95%. We find that the repairs resulted in fuel specific NOx emissions that are comparable or slightly lower than in-use light and medium-duty diesel trucks measured in Denver in 2020 indicating the repairs were a success.