Efficiency of Retrofit Systems on Reducing Ultrafine Particles and Other Pollutants Emitted by Diesel-powered School Buses
QUNFANG ZHANG, Shusen Liu, Yifang Zhu
Texas A&M University-Kingsville
Abstract Number: 209
Preference: Platform Presentation
Last modified: April 29, 2010
Working Group: Aerosol Exposure
Retrofit is one of the recommended methods for currently in-used diesel school buses to reduce children's exposure to diesel exhaust. To evaluate the efficiency of retrofit systems, this study measured both tailpipe emission and in-cabin air quality of school buses before and after retrofit. Six school buses were selected to cover different characteristics of currently in-used school buses. Two types of retrofit systems, diesel oxidation catalyst (DOC) and spiracle crankcase filtration system (CFS), were installed in each bus. Pre- and post-retrofitted tailpipe emissions and in-cabin air pollutant levels were measured when idling in the test garage. Then each bus was driven on two real pick-up/drop off routes with air condition on in the morning and off in the afternoon. Air pollutant concentrations inside buses as well as in the surrounding ambient air were measured before and after retrofit. The parameters monitored include the number concentration and size distribution of ultrafine particles (UFPs, diameter < 100 nm), total particle number concentration, PM$_2.5, Black Carbon (BC), CO and CO$_2. The results showed DOC and CFS achieved the average reduction of 20% and 31% on tailpipe total particles, respectively. With both DOC and CFS installed, tailpipe total particles decreased 48%. Similar reduction was also observed for PM$_2.5 and BC. However, no unequivocal decrease of air pollutants inside school buses was observed after retrofit. Similar results were measured on roadways. This suggests that the dominant source of the in-cabin air pollutant was not from school bus itself but ambient air. Statistical analysis showed the effects of AC unit and the surrounding air pollutant concentrations played more important roles in determining in-cabin air quality of school buses than retrofit system.