Department of Chemistry and Biochemistry, University of Denver , Denver, Colorado 80208, United States.
Department of Chemistry, University of Puget Sound , Tacoma, Washington 98416, United States.
Environ Sci Technol. 2016 May 17;50(10):5405-11. doi: 10.1021/acs.est.6b00717. Epub 2016 May 3.
State and local agencies in the United States use activity-based computer models to estimate mobile source emissions for inventories. These models generally assume that vehicle activity levels are uniform across all of the vehicle emission level classifications using the same age-adjusted travel fractions. Recent fuel-specific emission measurements from the SeaTac Airport, Los Angeles, and multi-year measurements in the Chicago area suggest that some high-mileage fleets are responsible for a disproportionate share of the fleet's emissions. Hybrid taxis at the airport show large increases in carbon monoxide, hydrocarbon, and oxide of nitrogen emissions in their fourth year when compared to similar vehicles from the general population. Ammonia emissions from the airport shuttle vans indicate that catalyst reduction capability begins to wane after 5-6 years, 3 times faster than is observed in the general population, indicating accelerated aging. In Chicago, the observed, on-road taxi fleet also had significantly higher emissions and an emissions share that was more than double their fleet representation. When compounded by their expected higher than average mileage accumulation, we estimate that these small fleets (<1% of total) may be overlooked as a significant emission source (>2-5% of fleet emissions).
美国的州和地方机构使用基于活动的计算机模型来估算移动源排放物的清单。这些模型通常假设所有使用相同年龄调整后的行驶分数的车辆排放水平分类的车辆活动水平是均匀的。最近在西雅图机场、洛杉矶进行的燃料特定排放测量以及在芝加哥地区进行的多年测量表明，一些高里程车队负责车队排放的不成比例份额。与一般人群中的类似车辆相比，机场的混合动力出租车在第四年的一氧化碳、碳氢化合物和氮氧化物排放量大幅增加。机场班车的氨排放量表明，催化剂还原能力在 5-6 年后开始减弱，比一般人群观察到的速度快 3 倍，表明加速老化。在芝加哥，观察到的道路出租车车队的排放量也明显更高，其排放量份额是车队代表的两倍多。考虑到它们预期的平均里程积累更高，我们估计这些小车队（<1%的车队）可能会被忽视，成为一个重要的排放源（>2-5%的车队排放量）。
