Department of Environmental Health Sciences, University of California Los Angeles, Los Angeles, California 90095-1772, United States.
Environ Sci Technol. 2011 Aug 1;45(15):6475-82. doi: 10.1021/es201070t. Epub 2011 Jul 8.
This study evaluated the performance of retrofit systems for diesel-powered school buses, a diesel oxidation catalyst (DOC) muffler and a spiracle crankcase filtration system (CFS), regarding ultrafine particles (UFPs) and other air pollutants from tailpipe emissions and inside bus cabins. Tailpipe emissions and in-cabin air pollutant levels were measured before and after retrofitting when the buses were idling and during actual pick-up/drop off routes. Retrofit systems significantly reduced tailpipe emissions with a reduction of 20-94% of total particles with both DOC and CFS installed. However, no unequivocal decrease was observed for in-cabin air pollutants after retrofitting. The AC/fan unit and the surrounding air pollutant concentrations played more important roles for determining the in-cabin air quality of school buses than did retrofit technologies. Although current retrofit systems reduce children's exposure while waiting to board at a bus station, retrofitting by itself does not protect children satisfactorily from in-cabin particle exposures. Turning on the bus engine increased in-cabin UFP levels significantly only when the wind blew from the bus' tailpipe toward its hood with its windows open. This indicated that wind direction and window position are significant factors determining how much self-released tailpipe emissions may penetrate into the bus cabin. The use of an air purifier was found to remove in-cabin particles by up to 50% which might be an alternative short-to-medium term strategy to protect children's health.
本研究评估了用于柴油动力校车的 retrofit 系统的性能，包括柴油机氧化催化剂 (DOC) 消音器和旋流曲柄箱过滤系统 (CFS)，以评估其从排气管排放和车内对超细颗粒 (UFPs) 和其他空气污染物的影响。在安装 DOC 和 CFS 后，在车辆怠速和实际接送路线期间，测量了 retrofit 前后的排气管排放和车内空气污染物水平。 retrofit 系统显著减少了排气管排放，总颗粒物减少了 20-94%。然而， retrofit 后车内空气污染物并没有明显减少。空调/风扇单元和周围的空气污染物浓度对校车车内空气质量的影响比 retrofit 技术更为重要。尽管当前的 retrofit 系统可减少儿童在车站等候上车时的暴露量，但 retrofit 本身并不能充分保护儿童免受车内颗粒物的暴露。只有当风吹向巴士的排气管并打开车窗时，打开巴士引擎才会显著增加车内的 UFP 水平。这表明风向和车窗位置是决定有多少自排放的排气管排放物可能渗透到巴士车厢内的重要因素。发现空气净化器可去除车内颗粒物高达 50%，这可能是一种保护儿童健康的短期到中期替代策略。
