Formaldehyde emissions variability in light-duty and heavy-duty diesel trucks under real-world conditions

Recent studies have indicated that diesel trucks could be significant sources of atmospheric formaldehyde (HCHO), which has detrimental effects on both the environment and human health. However, the variability of real-world HCHO emissions from different types of diesel trucks relating to driving conditions remains insufficiently explored. This study conducted real-world driving emission (RDE) tests on 19 light-duty (LDDTs) and heavy-duty diesel trucks (HDDTs) to assess emission variability. Results revealed that LDDTs emitted substantially higher levels of HCHO compared to HDDTs, with emissions up to 7 times higher under the China VI emission standard. Higher speeds during real-world driving and the smaller maximum engine torque of LDDTs might partly contribute to the increased emissions. The lack of application of after-treatment devices, especially diesel oxidation catalyst technology, primarily results in higher HCHO emissions from LDDTs. The established relationships between HCHO emissions and VSP provide a valuable basis for improving the quantification and modeling of vehicular HCHO emissions. These findings emphasize the future need to introduce HCHO-specific limits in vehicle emission standards, particularly targeting LDDTs. Enhancing aftertreatment requirements and incorporating VSP-based modeling frameworks into emission quantification will be essential for effectively controlling vehicle HCHO emissions and reducing their environmental and health impacts.