Background

Air pollution is a major health concern in worldwide. Non-methane volatile organic compounds (NMVOCs) are precursors of secondary air pollutants, with road transport being responsible of ~ 90% for the EU-27’s NMVOCs transport emissions in 2021. A series of VOC emissions from 17 modern gasoline, Diesel and Plug-in hybrid (PHEV) vehicles were investigated under various driving conditions and temperatures. All tested vehicles meet the latest European emission standard (Euro 6d and Euro 6d-TEMP). The different VOC species were measured with a Fourier-Transform Infrared Analyzer (FTIR).

Results

Diesel vehicles presented the lowest VOC emissions, while PHEVs operating in charge sustaining mode, with a depleted battery, exhibited very similar behavior to conventional gasoline. Among the VOCs, C₅ compounds were the primary contributors to total NMVOCs over WLTC at 23 °C for gasoline and PHEV vehicles. A proportional increase in VOC emissions at colder temperatures, affecting all the studied species, was observed. Significant increases were observed for Aromatics, with an important contribution of < C₅ as well. On the other hand, VOC emissions from Diesel vehicles were consistently low and little affected by temperature, except for Aldehydes in tests at − 7 °C. VOC emissions primarily occurred during cold starts, with urban cycle showing higher emission factors due to its shorter distance. VOC emissions remained consistently low during the highway cycle, highlighting a significant reduction in VOC emissions once the after-treatment system (ATS) was warmed up, even under demanding conditions. In Diesel vehicles, total VOCs measured with the FTIR exhibited a slight tendency to exceed Total Hydrocarbons (THC) measured with a Flame Ionization Detector (FID), while for gasoline vehicles and PHEVs, the trend was temperature-dependent.

Conclusions

In summary, the study shows that VOC emissions from Diesel vehicles are significantly lower compared to modern gasoline and PHEV vehicles. Moreover, gasoline and PHEV vehicles exhibit similar levels and emission profiles of VOC emissions. Additionally, ambient temperatures and driving conditions have a significant impact on VOC emissions for all the powertrain technologies investigated.