AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Relative Contributions of Self-Pollution and On-Road-Pollution to Children’s Exposure in School Buses
EON LEE, Yifang Zhu, University of California, Los Angeles
Abstract Number: 183 Working Group: Indoor Aerosols
Abstract Previous studies have shown children are exposed to high levels of PM$_(2.5), black carbon (BC), and ultrafine particle (UFP, diameter <= 100 nm) inside school buses. Both surrounding vehicle emissions from the roadway (i.e., on-road-pollutions) and school bus’ own emissions contribute to the exposure levels. While many studies have reported the presence of self-pollution in schools buses; the relative contributions between on-road-pollution and self-pollution is unknown. This study investigated under what conditions and to what extend self-pollution becomes more important than on-road-pollution. We estimated self-pollution rates inside six school buses and assessed the associated changes of spatial concentration distributions at increased driving speeds. The selected school buses include a wide range of model year, passenger capacity, cabin volume, and engine/exhaust tail-pipe locations. We measured the number concentration and size distributions of UFPs, PM$_(2.5), BC, CO$_2, and CO levels concurrently in and out of school buses. In-cabin measurements were conducted at breathing zones in the front, center, and back of school buses. Statistical regression analyses were conducted to estimate self-pollution rates for UFPs, PM$_(2.5), and BC. This study found high self-pollution rates of UFPs, PM$_(2.5), and BC in the school buses. On local streets, self-pollution makes in-cabin/on-road concentration (I/O) ratios as high as ~1.5 for UFPs and slightly less for PM$_(2.5) and BC. In comparison, on freeways, the I/O ratio was ~1.0 because of high air exchange rates and the infiltration of high-concentration of pollutants. Self-pollution dominates spatial concentration distributions of in-cabin pollutants. The spatial concentrations were substantially decreased at all three monitoring points at high driving speeds due to increased air exchange rates. The findings in this study suggest that self-pollution in school buses depends on self-pollution source strength, ambient concentration, and driving speed.