The next challenge in emissions control for heavy-duty diesel vehicles: From NOx to N2O

• Published in: Environmental pollution (1987) 2024-12, Vol.363 (Pt 2), p.125269, Article 125269
• Main Authors: Chen, Hongfei, He, Liqiang, Ji, Liang, Wang, Junfang, Sun, Nannan, Zhang, Rongshuo, Wei, Yangbing, Li, Tengteng, Zhong, Xianglin, Lv, Zhihua, Zhu, Rencheng, Li, Gang
• Format: Article
• Language: English
• Subjects: Dual selective catalytic reduction (dual SCR); Environmental conditions; Heavy-duty diesel vehicles (HDDVs); Nitrogen oxide (NOx); Nitrous oxide (N2O)
• ISSN: 0269-7491; 1873-6424; 1873-6424
• DOI: 10.1016/j.envpol.2024.125269

Vehicle emissions are a major source of greenhouse gases globally. Dual selective catalytic reduction (SCR), an advanced version of single SCR, is crucial under stricter nitrogen oxide (NOx) emission standards for heavy-duty diesel vehicles (HDDVs). However, the emission characteristics of nitrous oxide (N2O), a byproduct of SCR and a potent greenhouse gas, remain unclear. This study investigates the N2O emissions from HDDVs equipped with single or dual SCR systems using heavy-duty chassis dynamometers under various ambient temperatures, altitudes, and loading masses. The results showed that the brake-specific emissions (EFb) of N2O from HDDVs with single and dual SCRs were 76.28–269.65 mg/kWh and 147.50–170.22 mg/kWh, respectively. Notably, the dual SCR-equipped HDDV emitted 6–22 times more N2O than NOx under all tested conditions. As ambient temperature increased from −10 °C to 25 °C and from 25 °C to 40 °C, the average distance-based emission factors (EFd) of N2O for the single SCR-equipped HDDV increased by 87.73% and 48.26%, respectively. However, the variation was not significant for the dual SCR-equipped HDDV. Under half- and full-load conditions, the average EFd of N2O for the single SCR-equipped HDDV increased by 47.57% and 110.92%, respectively, compared to those without loading. Similarly, N2O emissions for dual SCR-equipped HDDV increased by 41.40% and 65.37% under the same loading variations. As altitude increased from 0 m to 3000 m, the average EFd of N2O for the single SCR-equipped HDDV decreased by 64.31%. Additionally, N2O emissions were significantly affected by SCR temperature, engine power, and nitric oxide (NO)/nitrogen dioxide (NO2) ratio. These findings are crucial for setting future greenhouse gas limits of HDDVs and informing carbon reduction strategies. [Display omitted] •Exhaust N2O, a greenhouse gas, from HDDVs with single/dual SCR was analyzed.•The dual SCR-equipped HDDV emitted more than ten times as much N2O as NOx.•N2O emissions of single SCR were clearly positively correlated with temperature.•More N2O was emitted from HDDVs with single/dual SCR under higher loads.•N2O emissions at the altitude of 3000 m decreased by 64% compared to 0 m.