As part of the Zero Pollution Action Plan of the Green Deal, the European Commission has set the goal of reducing the number of premature deaths caused by fine particulate matter (PM2.5) by at least 55% by 2030, compared to 2005 levels. To achieve this, the European Commission aims to introduce stricter limits. In urban areas, road transport is a significant source of PM emissions. Vehicle PM originates from engine exhaust and from tire, brake and road wear, as well as from road dust resuspension. In recent decades, the application of stringent emission limits on vehicle exhaust has led to the adoption of technologies capable of strongly reducing PM emissions at the tailpipe. Further, the progressive electrification of vehicle fleets will lead to near-zero exhaust PM emissions. On the other hand, non-exhaust PM emissions have increased in recent years following the proliferation of sport utility vehicles (SUVs), whose numbers have jumped nearly tenfold globally, and electric vehicles, as these vehicles tend to be heavier than corresponding conventional and older internal combustion engine light-duty vehicles. This shift has resulted in a more modest reduction in PM10 and PM2.5 emissions from the transport sector compared to other pollutants (−49% and −55%, respectively, from 1990 to 2020). This report aims to provide an up-to-date overview of non-exhaust PM characterization, drawing insights from the recent scientific literature to address this critical environmental and public health challenge.

In the last years, the in-use emissions of vehicles are measured on the road with portable emissions measurement systems (PEMS). PEMS cannot measure as accurately as the laboratory grade equipment, and studies on their measurement uncertainty have continued since their appearance in the market. In this study we compared PEMS to laboratory grade equipment in Italian laboratories testing a diesel “Golden” (i.e., reference) vehicle for two consecutive years. The results showed equal means of PEMS and laboratory grade equipment for carbon dioxide (CO₂), nitrogen oxides (NO_x), and particle number (PN), with a variability of ±5 g/km for CO₂, ±10 mg/km for NO_x, and ±1 × 10¹¹ p/km for PN, which further decreased in the second year. For carbon monoxide (CO), the PEMS were on average 5–20 mg/km higher than the bags (variability ±40 mg/km). The main conclusion of this study is that PEMS are accurate under controlled laboratory ambient conditions, without any indications of significant bias.