Unregulated particle and VOC emissions from comparable diesel, gasoline and natural gas vehicles

The use of Natural Gas for Vehicles (NGV) is increasing due to estimated positive impacts on exhaust emissions and carbon footprint. However, significant emissions of unregulated particles in the ultrafine range have been reported in the literature. Significant variations have also been observed, but data is still lacking to thoroughly describe NGV emissions. This is particularly true for some vehicle categories such as light commercial vehicles. A clear need therefore exists to additionally document the NGV emissions, especially unregulated compounds with health or environmental effects such as ultrafine particles and Volatile and Intermediate-Volatility Organic Compounds (VOCs/IVOCs). This study presents the emissions of methane, regulated gases, total particles from 5.6 nm with size distribution, and VOCs/IVOCs. It focuses on NGV, diesel and gasoline passenger cars and light commercial vehicles with comparable technical characteristics. Results show that during regeneration phases, ultrafine particle emissions from gasoline vehicles with particle filters increase by factors 40 to 800. They also show high emissions of ultrafine particles from NGV, with significant shares of sub-23 and sub-10 nm particles (more than 2/3 of the emissions). The organics emitted by the NGV are less volatile than those from diesel or gasoline. Coupled with the significant sub-10 and sub-23 nm particles from NGV, this suggests that the particles could be partly semi-volatile. The NGV particle emissions might thus be underestimated with current normative protocols. In addition to measuring particles from 10 nm in the upcoming Euro 7 norm, this study indicates that quantifying semi-volatile particles could help better describe vehicular emissions, especially for NGV vehicles. • PN and VOCs were measured for passenger cars and light commercial vehicles. • Comparable diesel, gasoline and natural gas vehicles were tested. • Natural gas PN are mostly below 23 or 10 nm, overall smaller than diesel or gasoline. • VOC emissions suggest that natural gas PN could be partly semi-volatile. • Natural gas PN could be significantly underestimated with current norms.