Li Chunlei, Nguyen Quyen, Ryan Patrick H, Lemasters Grace K, Spitz Henry, Lobaugh Megan, Glover Samuel, Grinshpun Sergey A
Department of Environmental Health, University of Cincinnati, Cincinnati, OH, USA.
J Environ Monit. 2009 May;11(5):1037-42. doi: 10.1039/b819458k. Epub 2009 Feb 27.
Millions of children attending US schools are exposed to traffic-related air pollutants, including health-relevant ultrafine aerosols generated from school buses powered with diesel fuel. This case study was established in a midwestern (USA) metropolitan area to determine the concentration and elemental composition of aerosol in the vicinity of a public school during morning hours when the bus traffic in and out of the adjacent depot was especially intense. Simultaneous measurements were performed at a control site. The ambient aerosol was first characterized in real time using a particle size selective aerosol spectrometer and then continuously monitored at each site with a real-time non-size-selective instrument that detected particles of 20 nm to >1 microm. In addition, air samples were collected with PM2.5 Harvard Impactors and analyzed for elemental composition using the X-ray fluorescence technique (for 38 elements) and thermal-optical transmittance (for carbon). The measurements were conducted during two seasons: in March at ambient temperature around 0 degrees C and in May when it ranged mostly between 10 and 20 degrees C. The particle number concentration at the test site exhibited high temporal variability while it was time independent at the control site. Overall, the aerosol particle count at the school was 4.7 +/- 1.0 times (March) and 2.2 +/- 0.4 times (May) greater than at the control site. On some days, a 15 min-averaged particle number concentration showed significant correlation with the number of school bus arrivals and departures during these time intervals. On other days, the correlation was less than statistically significant. The 3 h time-averaged particle concentrations determined in the test site on days when the school buses operated were found to be more than two-fold greater (on average) than those measured on bus-free days at the same location, and this difference was statistically significant. Overall, the data suggest a possible association between the number of detected aerosol particles and the school bus traffic intensity. Analysis of the filter samples collected at the school site between 6:00 and 9:00 AM revealed higher concentrations of elemental carbon as compared to the control site (2.8 +/- 0.9 times in March and 3.1 +/- 1.1 times in May). The data collected in this case study suggest that school buses significantly contribute to exposure of children to aerosol pollutants (including diesel exhaust particles) in the school vicinity.
数百万在美国上学的儿童暴露于与交通相关的空气污染物中，包括由柴油驱动的校车产生的与健康相关的超细气溶胶。本案例研究在（美国）中西部一个大都市地区开展，旨在确定一所公立学校附近早晨时段气溶胶的浓度和元素组成，此时进出相邻公交场站的公交交通尤为繁忙。在一个对照站点同时进行了测量。首先使用粒径选择性气溶胶光谱仪对环境气溶胶进行实时表征，然后在每个站点使用实时非粒径选择性仪器对粒径为20纳米至大于1微米的颗粒进行连续监测。此外，使用PM2.5哈佛撞击器采集空气样本，并使用X射线荧光技术（针对38种元素）和热光透过率（针对碳）分析其元素组成。测量在两个季节进行：3月环境温度约为0摄氏度，5月环境温度大多在10至20摄氏度之间。测试站点的颗粒数浓度呈现出较高的时间变异性，而对照站点的颗粒数浓度与时间无关。总体而言，学校的气溶胶颗粒计数在3月是对照站点的4.7±1.0倍，在5月是对照站点的2.2±0.4倍。在某些日子里，15分钟平均颗粒数浓度与这些时间间隔内校车的到达和离开数量显示出显著相关性。在其他日子里，相关性低于统计学显著性。发现在校车运营的日子里，测试站点3小时时间平均颗粒浓度（平均）比在同一地点无校车日子里测量的浓度高出两倍多，且这种差异具有统计学显著性。总体而言，数据表明检测到的气溶胶颗粒数量与校车交通强度之间可能存在关联。对上午6点至9点在学校站点采集的滤膜样本分析显示，与对照站点相比，元素碳浓度更高（3月为2.8±0.9倍，5月为3.1±1.1倍）。本案例研究收集的数据表明，校车对儿童在学校附近暴露于气溶胶污染物（包括柴油尾气颗粒）有显著影响。
