ABSTRACT

Over the past decade, efforts to reduce emissions of particulate matter (PM) and oxides of nitrogen (NO + NO₂, or NO_x) from heavy-duty diesel vehicles (HDDVs) have led to the widespread adoption of both Diesel Particulate Filters (DPFs) to control PM and Selective Catalytic Reduction (SCR) to control NO_x. We evaluated the performance of DPFs and SCR with 13,327 real-world fuel-based Black Carbon (BC) and NO_x emission factors from 9,167 unique heavy-duty vehicles (primarily HDDVs) measured at four sites in California (two ports, two highways) from 2011 to 2018. BC emission factors have decreased by 90% during the past decade. At the same time, BC distributions have become increasingly skewed toward “high-emitters” – e.g., the portion of the HDDV fleet responsible for half of all BC emissions has decreased from ~16% to ~3%. NO_x emission factors have also decreased over the past decade, but by only 31%. They remain roughly five times greater than in-use thresholds.We examined changes in BC and NO_x emissions with engine age. BC emissions from DPF-only trucks decreased slightly but insignificantly, by 6 ± 15 mg/kg fuel per year, while for DPF+SCR trucks they increased by 5 ± 3. These changes are less than 5% of in-use thresholds. The annual increase in NO_x emissions with age was much greater: 1.44 ± 0.28 g/kg for older SCR trucks without on-board diagnostic (OBD) capabilities and 0.48 ± 0.35 for newer trucks with OBD, roughly 20– 50% of in-use thresholds. Paired t-tests on the over 600 vehicles that were observed in multiple campaigns were consistent with these results. Observed changes in BC emissions with age were best fit with a “gross emitter” model assuming an annual DPF failure rate of 0.83 ± 0.01% for DPF-only trucks and 0.56 ± 0.01% for DPF+SCR trucks.Implications: These observations of real-world HDV emission factors have several major implications for regulatory efforts to reduce them. The increasing importance of a relatively small number of high BC emitters suggests that widespread sampling of the on-road fleet will be necessary to identify these vehicles. On the other hand, the much more ubiquitous deterioration in NO_x control measures may be better addressed by incorporating on-board diagnostic systems, with telematic data transfer when possible, into inspection and maintenance programs. These NO_x observations also highlight the need for strengthening heavy-duty SCR durability demonstration requirements.

摘要

在过去的十年中，为减少重型柴油车 (HDDV)的颗粒物 (PM) 和氮氧化物 (NO + NO ₂或 NO _x )排放的努力导致两种柴油微粒过滤器得到广泛采用（ DPFs) 来控制 PM 和选择性催化还原 (SCR) 来控制 NO _x。我们用 13,327 种真实世界的燃料基黑碳 (BC) 和 NO _x评估了 DPF 和 SCR 的性能2011 年至 2018 年在加利福尼亚州的四个地点（两个港口、两条高速公路）测量的 9,167 辆独特的重型车辆（主要是 HDDV）的排放因子。BC 排放因子在过去十年中下降了 90%。与此同时，BC 分布越来越倾向于“高排放者”——例如，占所有 BC 排放量一半的 HDDV 车队部分已从约 16% 下降到约 3%。NO _x排放因子在过去十年中也有所下降，但仅下降了 31%。它们仍然是使用阈值的大约五倍。我们检查了 BC 和 NO _{x 的}变化排放与发动机老化。仅 DPF 卡车的 BC 排放量略有下降，但不显着，每年减少 6 ± 15 mg/kg 燃料，而 DPF + SCR 卡车的 BC 排放量增加了 5 ± 3。这些变化不到使用阈值的 5%。随着车龄的增长，每年 NO _x排放量的增加要大得多：没有车载诊断 (OBD) 功能的旧式 SCR 卡车为 1.44 ± 0.28 g/kg，具有 OBD 功能的新型卡车为 0.48 ± 0.35，大约占总排放量的 20-50%。使用阈值。在多个活动中观察到的超过 600 辆车的配对t检验与这些结果一致。观察到的 BC 排放随车龄的变化最适合“总排放量”模型，假设每年 DPF 故障率仅 DPF 卡车为 0.83 ± 0.01%，DPF + SCR 卡车为 0.56 ± 0.01%。影响：这些对现实世界 HDV 排放因子的观察对减少它们的监管工作有几个主要影响。相对少数高 BC 排放者的重要性日益增加，这表明有必要对公路车队进行广泛抽样以识别这些车辆。在另一方面，在NO的更加普遍存在的恶化_X的控制措施，可以更好地诊断系统包含板载寻址，同时远程信息数据传送时可能的，成的检查和维护程序。这些 NO _x观察结果还强调了加强重型 SCR 耐久性演示要求的必要性。