Validity of evaluation by solid particle number measurement at periodic technical inspection and in real-world conditions of diesel particulate filter

Regulated emissions in a type approval test (TAT) and a tailpipe solid particle number (SPN) concentration measurement, which has been introduced in the periodic technical inspection (PN-PTI) in some European countries, were measured for a diesel passenger car equipped with a diesel particulate filter (DPF). The correlations between SPN in TAT and the PN-PTI were good, and the European recommended limit for PN-PTI was almost equal to the regulatory limit of SPN in the TAT, suggesting the validity of evaluating exhaust performance by PN-PTI. In addition, in a real-world evaluation campaign conducted at several PTI stations in Japan, exhaust emissions from light-duty and heavy-duty vehicles under inspection were monitored by PN-PTI devices. A total of 582 DPF diesel vehicles were checked, and 18.2 % of them were found to have problems with their DPFs.