Particle emissions from diesel engines-looking beyond carbon soot emissions

Particulate matter (PM) emissions involve a complex mixture of solid and liquid particles suspended in a gas, where it is noted that PM emissions from diesel engines are a major contributor to the ambient air pollution problem. Whilst epidemiological studies have shown a link between increased ambient PM emissions and respiratory morbidity and mortality, studies of this design are not able to identify the PM constituents responsible for driving adverse respiratory health effects. There is strong evidence that organic compounds are most responsible for the toxicity of airborne particles. Some recent toxicological studies indicate that PM related reactive oxygen species (ROS) and the resulting oxidative stress they engender may be implicated in the instigation of the adverse health effects. Taking this into account we have explored the correlation between particulate organic material and the potential of diesel PM to cause oxidative stress, as measured by the concentration of ROS. We find that the oxidative potential of diesel PM although proportional to the total organic content in certain cases shows a much higher correlation with the oxygenated organic fraction. This highlights the importance of knowing the surface chemistry of particles for assessing their health impacts. It also sheds a light onto new aspects of combustion particulate emissions that should be taken into account when establishing relevant metrics for health implications of emissions from various future fuels.