ARTICLE pubs.acs.org/est
Performance of School Bus Retrofit Systems: Ultrafine Particles and Other Vehicular Pollutants Qunfang Zhang and Yifang Zhu Department of Environmental Health Sciences, University of California Los Angeles, 650 Young Drive South, Los Angeles, California 90095-1772, United States
bS Supporting Information ABSTRACT: 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-tomedium term strategy to protect children’s health.
’ INTRODUCTION Although school buses are the safest way to transport school children, diesel pollution levels in and around school buses were found to be much higher than background levels.1 3 Ultrafine particles (UFPs, diameter
