Studies of Self-Pollution in Diesel School Buses: Methodological Issues

Abstract

Considerable interest has focused on levels of exhaust emissions in the cabins of diesel-powered school buses and their possible adverse health effects. Significantly different policy and engineering issues would be raised if compelling evidence found that in-c-cabin contamination was due to self-pollution from bus emissions, rather than ambient pollution, neighboring vehicles, and/or re-entrained road dust. We identified 19 reports from 11 studies that measured diesel exhaust particulate in the cabins of 58 school bus of various type. Studies were evaluated in light of their experimental design, their data quality, and their capacity to quantify self-pollution. Only one study had a true experimental design, comparing the same buses with and without emission controls, while four others used intentional tracers to quantify tailpipe and/or crankcase emissions. Although definitive data are still lacking, these studies suggest that currently available control technologies can nearly eliminate particulate self-pollution inside diesel school buses.

Keywords:

• diesel
• diesel emissions
• diesel exhaust
• exposure assessment
• school bus
• tracer

ACKNOWLEDGMENTS

Financial support was provided by International Truck and Engine Corporation, which did not participate in the design of this study or in the collection, management, analysis or interpretation of the data. Preparation and editing of the manuscript were performed solely by the authors.

Notes

^A One of 11 buses used diesel to idle and CNG while moving.

^B A single bus was tested without and then retrofitted with various emission controls.

^C Two typical diesel buses and two high emitting diesel buses.

^D Ambient particle count at one of the major roadways.

^A = > 0.003 μ m.

^B = 0.03–0.8 μ m, 0.3–0.5 μ m; 0.3–10 μ m.

^C = < 2.5 μ m.

^D = 0.01–1.0 μ m.

^E = ultrafine.

^A LOD: Limit of detection ranged from 4.1–4.9 μ g/m³ depending on sampling duration.

^A Ref. 21.

^B Refs. 30,31.

^C Refs. 23–27.

^A Bus configurations: DOC = diesel oxidation catalyst and convention fuel; DPF = diesel particulate filter; Spiracle = closed-crankcase filtration device; ULSD = ultra-low sulfur diesel fuel.

^B Particles 0.01–1.0 μ m.