Across the pond, the Dutch have passed a new form of testing vehicles equipped with a diesel particulate filter (DPF). The new periodic technical inspection (PTI) test relies on a particle counting instrument which can detect DPF removal, alteration, or malfunction. The new test is said to replace smoke opacity tests (which are said to be ineffective on modern diesel engines) or the use of OBD data to diagnose DPF problems during periodic technical inspections. The particle counting device collects its number measurement at the tailpipe, and the PN rejection standard has been locked in at 1,000,000 cm3 for all diesel vehicles (vs. 250,000 cm3 for Euro 5b+ vehicles under the 2019 rule).Source:http://dieselnet.com/news/2021/01npti.php