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Assessing Children's Exposure to Ultrafine Particles and Other Air Pollutants in School Buses and at Schools


Increasing evidence has demonstrated toxic effects of ultrafine particles (UFPs, diameter < 100 nm). Children are particularly at risk due to their immature respiratory systems and greater breathing rates per body weight. This study aims to assess children's exposure to UFPs and other air pollutants in school buses and at schools. 24 school buses were employed to represent commonly used school buses in the United States. UFPs and other air pollutants in and around school buses were measured while idling and driving on roadways. The performances of retrofit systems for diesel-power school buses, a diesel oxidation catalyst (DOC) muffler and a spiracle crankcase filtration system (CFS), were evaluated regarding UFP and other air pol lutants from tailpipe emissions and inside bus cabins. UFPs and other air pollutants was examined simultaneously inside and outside of different indoor microenvironments at five schools with different ventilation systems. When driving on roadways, the important factors for in-cabin total particle number concentrations included engine age, window position, driving speed, driving route, bus operation and passenger load. Idling increased total particle number concentration near the school buses under all scenarios, by a factor of up to 26.0. Depending on wind direction and window position, idling increased total particle number concentration inside the school buses by a factor of 1.3 - 2.9, with the majority occurring in the size range of 10-30 nm. Retrofit systems significantly reduced tailpipe emissions by 20% - 94% for total particle number concentration with both DOC and CFS installed. No unequivocal decrease was observed for in-cabin air pollutants after retrofitting. The AC/fan unit and the surrounding air played more important roles for determining in-cabin air quality than did retrofit technologies. The use of an air purifier was found to remove in-cabin particles by up to 50%. For the indoor microenvironments at schools, the most important factors affecting indoor total particle number concentration were related to various indoor sources. Without indoor sources, the indoor-to-outdoor (I/O) ratios for total particle number concentrations varied from 0.12 to 0.66 for the five ventilation systems studied. The I/O ratio decreased when the outdoor total particle number concentration increased.

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