Exposure Assessment of Diesel Bus Emissions

Maricela Yip,Aaron Wiegand,Pierre Madl,Werner Hofmann

doi:10.3390/ijerph2006030038

Abstract

The goal of this study was to measure ultrafine particle concentrations with diameters less than 1 mum emitted by diesel buses and to assess resulting human exposure levels. The study was conducted at the Woolloongabba Busway station in Brisbane, Australia in the winter months of 2002 during which temperature inversions frequently occurred. Most buses that utilize the station are fuelled by diesel, the exhaust of which contains a significant quantity of particle matter. Passengers waiting at the station are exposed to these particles emitted from the buses. During the course of this study, passenger census was conducted, based on video surveillance, yielding person-by-person waiting time data. Furthermore, a bus census revealed accurate information about the total number of diesel versus Compressed Natural Gas (CNG) powered buses. Background (outside of the bus station) and platform measurements of ultrafine particulate number size distributions were made to determine ambient aerosol concentrations. Particle number exposure concentration ranges from 10 and 40 to 60% of bus related exhaust fumes. This changes dramatically when considering the particle mass exposure concentration, where most passengers are exposed to about 50 to 80% of exhaust fumes. The obtained data can be very significant for comparison with similar work of this type because it is shown in previous studies that exhaust emissions causes cancer in laboratory animals. It was assumed that significant differences between platform and background distributions were due to bus emissions which, combined with passenger waiting times, yielded an estimate of passenger exposure to ultrafine particles from diesel buses. From an exposure point of view, the Busway station analyzed resembles a street canyon. Although the detected exhaust particle concentration at the outbound platform is found to be in the picogram range, exposure increases with the time passengers spend on the platform along with their breathing frequency.

Highlights

Despite considerable amounts of basic research, neither the formation of diesel particulate matter (DPM) in the combustion chamber, nor its physico-chemical properties or human health effects are fully understood at present
From the bus census made in this study, it is known that the bulk of vehicles frequenting the Woolloongabba Busway station are diesel-powered buses
This study has shown that significant particle exposure concentrations to humans are present at the platform and are most likely to be found in similar settings for future studies of this kind

Summary

Introduction

Despite considerable amounts of basic research, neither the formation of diesel particulate matter (DPM) in the combustion chamber, nor its physico-chemical properties or human health effects are fully understood at present. Almost the entire fresh diesel exhaust particle mass is in the fine particle range of less than 1 μm in diameter Because of their minute sizes and hydrophobic properties, these particles are inhaled and eventually trapped within the bronchial and alveolar regions of the lung. Studies investigating the chemical and physical changes of diesel exhaust emissions suggest that there is little or no hygroscopic growth of primary diesel particles [1]. This observation suggests that the small size of DPM particles might be maintained upon inhalation, near the emission source, allowing these particles to reach the deeper portions of the respiratory tract. Since it is known that diesel exhaust contains organic matter

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