Non-exhaust gas and particle emissions of light-duty vehicles – Quantification under driving conditions in a sealed cabin

Abstract

Non-exhaust emissions have emerged as a pivotal contributor to vehicle emissions, as regulatory efforts persist in curtailing exhaust emissions. This research focused on the running-loss evaporative volatile organic carbon (VOC) and non-exhaust particle (NEP) emission factors (EFs) of a light-duty vehicle in the sealed housing. VOC concentrations demonstrated an upward trend with elevated vehicle temperatures and extended driving durations. Normalized over driving distance, the hot-start WLTC test exhibited the highest VOC EFs, about 617 μg/km, and the highest ozone formation potential (OFP) value of 1.75 mgO3/km. Toluene and xylene were the main pollutants contributing to the OFP value across all tests. Evaluating EFs of various evaporative emission forms in mg/h, the BTEXs EF of running-loss tests was recorded at 10.2 mg/h, comparable to diurnal-breathing tests but significantly lower than hot-soak tests. Additionally, particles within the 10–23 nm range consistently dominated total NEP above 10 nm. Particle number (PN) concentrations of 10–23 nm particles exhibited a sharp increase under intense driving conditions and a slow decrease under other driving conditions. The results suggested a continuous consumption of smaller particles, leading to their coalescence into larger particles. The EF of NEP above 23 nm in the US06_4 test was 1.72 × 1012 #/km, surpassing the current exhaust particle emission limit. Consequently, NEP has been a major vehicle particle source of greater concern than exhaust particles.