Practical, low-cost integrity testing of diesel particle filters using remote sensing measurement at the campus entrance gate

This work investigates the detection of defunct or absent diesel particle filters by drive-through remote sensing measurement at the Czech University of Life Sciences main vehicular entrance gate. An exhaust sample was collected by a line attached to the road surface in the center of the travel lane. A non-volatile particle number (nvPN) counter and electric mobility particle size classifier were used to measure particle number concentrations, and an FTIR analyzer was used to measure CO₂, CO, and NO concentrations. Of 59.7 % of 526 entering vehicles, peak CO₂ concentrations above 100 ppm were observed, suggesting that the entrance gate is ideal for sampling-style remote sensing measurements due to high signal strength and controlled spacing between vehicles. On 48 vehicles, the measurements were compared to a 10-s periodic technical inspection (PTI) style measurement of tailpipe nvPN concentrations at idle. The results indicate nearly absolute agreement in distinguishing diesel vehicles with and without a functional DPF, with one outlier with a relatively weak CO₂ signal and weak correlation between roadside nvPN and CO₂ concentrations. Using a linear regression approach to calculate the remote sensing emissions factors (EF) and restricting the data to those with peak CO₂ at least 100 ppm yielded an absolute agreement not only between tailpipe nvPN concentrations at idle and remote sensing nvPN EF but also between tailpipe nvPN and roadside concentration of both nvPN and total particle number in 25-560 nm size bins. The reported setup presents, in the authors' opinion, a relatively simple, robust, non-obtrusive, and practical means of checking DPF functionality in locations interested in excluding high emitters, such as university campuses, airports, large parking garages, national park entrances, and similar locations where entering vehicles are fully warmed up and not cooled down by extended waiting in line. Relatively strong CO₂ signal yielding high accuracy of detection of non-DPF diesels with laboratory instrument presents, in the opinion of the authors, a very high chance of successful exploitation of diffusion chargers, nvPN counters intended for PTI use in several EU countries, and other low-cost particle number sensors, with detection limit in thousands of #/cm³, and possibly low-cost black carbon monitors, along with a low-cost NDIR CO₂ sensor and a camera or other means of identifying individual tested vehicles, for detecting defunct diesel particle filters. The CO₂ signal alone can identify vehicles using internal combustion engines. Extending this measurement to CO and NO concentrations may also detect non-functional three-way and NOx-reducing catalysts, as demonstrated on three L-category vehicles, one quad, and two motorcycles. The setup also could be used as a drive-through, loaded-mode PTI test.