Aerosol Exposure at Schools during Morning Hours: Air Pollution Generated by School Buses

SERGEY A. GRINSHPUN, Chunlei Li, Michael Yermakov, Patrick H. Ryan, Grace K. LeMasters, Henry Spitz, Megan Lobaugh, Samuel Glover

University of Cincinnati, Cincinnati, OH, USA

     Abstract Number: 29
     Last modified: October 1, 2009

Abstract
Aproximately 24 million American students use school bus transportation. It is provided by about 600,000 buses, the majority of which is diesel fueled, potentially representing a significant source of exposure to traffic-related particles. Particles arising from traffic sources have been linked to various health effects, including asthma. However, very few studies attempted to address the effect of school bus emission on the ambient air quality at schools, and no safe levels of relevant exposures have been established for children. In this case study, performed in Cincinnati, Ohio, we determined the ambient particle number concentration and elemental composition at a large school during intense bus traffic. Identical measurements were simultaneously conducted at a control site. The ambient aerosol was characterized using a real-time Wide Range Particle Spectrometer (WPS) and then continuously monitored at each site with a P-Trak, which non-size-selectively detected particles of 20 nm to >1000 nm in real-time and through air sampling with PM2.5 Harvard Impactors. The latter generated filters, which were subjected to elemental analysis by the X-ray fluorescence technique as well as to the elemental and organic carbon analysis by thermal-optical transmittance. The measurements were performed during the winter and spring seasons.
The ambient aerosol was found to be greatly affected by the school bus traffic with respect to the number concentration and the PM2.5 elemental composition. The particle count at the school site exceeded that at the control site almost by 5-fold in winter when buses were continuously idling and over 2-fold in spring when there was less idling. On some days, a 15 min-averaged particle number concentration exhibited significant correlation with the number of school bus arrivals and departures during these time intervals. On other days, the correlation was not statistically significant, which pointed at an increased influence of mobile and stationary PM sources unrelated to school buses. At the test site, the 3-h-averaged particle concentration was more than 2-fold higher (on average) on days when the school buses operated as compared to bus-free days. Overall, the data indicated that there was an association between the number of detected aerosol particles and school bus traffic intensity. No statistically significant association was found between the particle concentration and the commuter traffic intensity at the school site, which suggested a dominant contribution of the school bus emission. The levels of elemental carbon in the PM2.5 samples collected at the school site exceeded those at the control site: 2.8-fold in winter and 3.1-fold in spring. The PM2.5 mass concentrations of other relevant chemical elements were also higher. We concluded that particulate emission from school bus exhaust (including ultrafine diesel particles) significantly contributes to the children’s short-term exposure at schools.
This study has been supported in parts through the Pilot Grant Program of University of Cincinnati Center for Sustainable Urban Engineering (2007 and 2008) and Grant No. R01 ES11170 from the National Institute of Environmental Health Sciences.