Unexpected higher emissions of nitrogenous compounds and formaldehyde during DPF regeneration in real driving emission test of China VI heavy-duty diesel trucks.

Heavy-duty diesel vehicles are important sources of air pollutants, yet gaseous emissions during diesel particulate filter (DPF) regeneration remain insufficiently characterized under real-world driving conditions. In this study, a portable emissions measurement system (PEMS) was used to quantify gaseous emissions from a China VI heavy-duty diesel truck during an on-road regeneration event. The instantaneous emissions and regeneration contributions of NO, NO2, N2O, and HCHO were systematically evaluated. All four pollutants exhibited pronounced emission peaks during regeneration, substantially exceeding those observed during non-regeneration driving. Emissions during regeneration accounted for 37%, 66%, 71%, and 78% of the total test emissions of NO, NO2, N2O, and HCHO, respectively. Elevated HCHO and nitrogenous compound emissions showed strong correlations with DPF inlet temperature during the heating and cooling phases. Assuming a 500-km regeneration interval, regeneration was estimated to occur over only 4.66%-5.99% of the vehicle's useful-life mileage, with scenario-based lifetime contributions reaching up to 38.36% and 25.76% of lifetime HCHO and NO2 emissions, respectively. These findings highlight that regeneration-related emissions can represent a substantial fraction of gaseous emissions for our tested vehicle, underscoring the importance of further considering such events in emission characterization and inventory development.