Department of Chemistry and Biochemistry, University of Denver , Denver, Colorado 80208, United States.
Environ Sci Technol. 2014 Dec 16;48(24):14822-7. doi: 10.1021/es5043518. Epub 2014 Nov 26.
The global economic recession of 2008-2010 severely depressed light-duty vehicle sales in the United States. On-road fleets observed with a remote vehicle exhaust sensor in 2013 at three historical sampling locations in Denver, Los Angeles, and Tulsa showed large reductions in the fleet fractions of 2009 model year vehicles of 40%, 38%, and 35%, respectively, when compared to prerecession 2007 levels with the light-duty truck category suffering the largest percentage declines. The fleet fraction for these ∼ 5 year old vehicles is normally reserved for vehicles more than twice their age. This resulted in a significant increase in the on-road freeway fleet age, which had been relatively stable. The fleet average age increased by two years in Denver and Los Angeles but only by one year in Tulsa, likely due to its faster economic recovery. Using fleet fractions from previous data sets, we estimated age-adjusted mean emissions increases for the 2013 fleet to be 17-29% higher for carbon monoxide, 9-14% higher for hydrocarbons, 27-30% higher for nitric oxide, and 7-16% higher for ammonia emissions than if historical fleet turnover rates had prevailed.
2008 年至 2010 年的全球经济衰退严重抑制了美国的轻型汽车销售。2013 年，在丹佛、洛杉矶和塔尔萨的三个历史采样点，使用远程车辆废气传感器对道路车队进行了观测，结果表明，与 2007 年经济衰退前的水平相比，2009 年车型的车队比例分别大幅下降了 40%、38%和 35%，其中轻型卡车类别的降幅最大。这些使用了大约 5 年的车辆的车队比例通常是为使用时间超过其两倍的车辆保留的。这导致道路高速公路车队的年龄显著增加，而车队的平均年龄在丹佛和洛杉矶增加了两年，但在塔尔萨仅增加了一年，这可能是由于其经济复苏较快。利用之前数据集的车队比例，我们估计 2013 年车队的经年龄调整后的平均排放量增加了 17-29%，一氧化碳增加了 9-14%，碳氢化合物增加了 27-30%，氮氧化物增加了 7-16%，而如果历史车队周转率保持不变，则排放量会更高。
