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 NO_x 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 NO_x 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. NO_x data from six recent European remote sensing campaigns (2021-2023) were analyzed. The findings suggest that NO_x 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 NO_x emission measurements with greater confidence.