ARTICLE pubs.acs.org/est
Volatile Properties of Particles Emitted by Compressed Natural Gas and Diesel Buses during Steady-State and Transient Driving Modes E. R. Jayaratne, N. K. Meyer,† Z. D. Ristovski,* and L. Morawska International Laboratory for Air Quality and Health (ILAQH), Institute of Health and Biomedical Innovation, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia ABSTRACT: Volatile properties of particle emissions from four compressed natural gas (CNG) and four diesel buses were investigated under steady-state and transient driving modes on a chassis dynamometer. The exhaust was diluted utilizing a full-flow continuous volume sampling system and passed through a thermodenuder at controlled temperature. Particle number concentration and size distribution were measured with a condensation particle counter and a scanning mobility particle sizer, respectively. We show that while almost all the particles emitted by the CNG buses were in the nanoparticle size range, at least 85% and 98% were removed at 100 and 250 °C, respectively. Closer analysis of the volatility of particles emitted during transient cycles showed that volatilization began at around 40 °C, with the majority occurring by 80 °C. Particles produced during hard acceleration from rest exhibited lower volatility than those produced during other times of the cycle. On the basis of our results and the observation of ash deposits on the walls of the tailpipes, we suggest that these nonvolatile particles were composed mostly of ash from lubricating oil. Heating the diesel bus emissions to 100 °C removed ultrafine particle numbers by 69 82% when a nucleation mode was present and just 18% when it was not.
1. INTRODUCTION Particle emission standards for motor vehicles are generally based on particle mass. After-treatment devices such as particulate filters fitted to modern vehicles can reduce the particle mass emissions considerably. However, this can often lead to the production of larger numbers of particles by homogeneous nucleation and condensation of the volatile gases as the exhaust dilutes and cools in the environment.1,2 These particles exist in the ultrafine size range (
