Detected or not? Remote sensing measurements from the latest Euro 6d vehicles across Europe.

Incorporating real-driving emission tests into type approval procedures has significantly reduced emissions from diesel passenger cars. Recent remote sensing studies suggest that NOx emissions from the latest Euro 6d series (including both Euro 6d-TEMP and Euro 6d) are extremely low, in some cases approaching zero. This study investigates whether these low NOx concentrations fall below the detection limits of remote sensing devices, potentially limiting the reliability of measured values. A method is proposed to estimate the limit of detection using electric vehicle measurements, which serve as low-emission references in the absence of calibration gases. NOx data from six recent European remote sensing campaigns (2021–2023) were analyzed. The findings suggest that NOx emissions from the latest Euro 6d series vehicles that are in good working order have reached the detection limit of OPUS RSD 5000 devices. This approach presents a practical framework for routinely determining the detection limits of remote sensing devices, improving quality assurance procedures and supporting the interpretation of ultra-low NOx emission measurements with greater confidence.