Nanoparticle counting for PTI: the dirty tail paradigm - a pragmatic proposal to strongly reduce urban PN pollution from combustion engine fleets

Abstract

Using solid particle number (PN) measurements in the European Periodic Technical Inspection (PTI) of diesel engines equipped with particulate filters was proposed by VERT in 2016 during the Dieselgate Hearing of the Federal Republic of Germany. An international working group developed the standards and instruments for this method over 3 years under the leadership of TNO and VERT, which were next implemented in four countries, Belgium, the Netherlands, Germany, and Switzerland, starting in 2022. PN measurement is now state of the art, enabling rapid and reliable detection of possible failures in particulate filters and the need for their immediate restoration. This paper expands on that successful experience, recommending that PN counting be used for control of PN emissions from all vehicles during PTI. It reviews results from a number of earlier studies on “high emitters” and shows some new data sets for gasoline engines. Five large vehicle fleets, diesel and gasoline, heavy-duty engines (HDE), light-duty vehicles (LDV), and non-road mobile machinery (NRMM), with and without emission aftertreatment were analyzed. It was observed that, while most vehicles in working fleets are clean (i.e., meet or often are far are below their corresponding emission limits), every fleet, however, contains some high emitters, about 4–8% of the fleet hereby termed “dirty tail” — diesel as well as gasoline engines. This small fraction dominates the PN emission of the entire fleet and may increase the overall PN emission of its corresponding fleet by more than tenfold over the level of the compliant vehicles! Experience indicates that PN emission may be a strong indicator of many different deteriorations in a combustion engine and thus can be used as a highly sensitive diagnostic signal to detect various engine or emission faults quickly and reliably. This is a new understanding of emission control of vehicle fleets: not by regulations for new vehicles only which apply for all vehicles but by selecting the high emitters and consequently repair or replace these relatively few vehicles to the extent desired in terms of emissions policy. Most countries have already implemented strong periodic technical inspection systems. We suggest to expand such tests by additionally measuring the particle number concentration in the exhaust gas of all vehicles for just 1 min, thereby detecting the high emitters. With consistent annual monitoring, this procedure will reduce urban particle pollution from combustion engines to one-tenth or lower, a significant contribution to reducing local health risks.