Composition of diesel exhaust varies with engine loading, producing differential health impact characteristics from the emissions

As noted in several prior posts, the study of the impact on diesel exhaust has focused on the PM10 and PM 2.5 profiles of the emissions. Recently, researchers argued that this view is too simplistic, and present an interesting study in support of their view.

The researchers analyzed the composition of diesel engine exhaust ("DEE") generated from a single-cylinder diesel generator operating under full (100%) or partial (55%) load. They also evaluated several health end-points in two strains of mice that inhaled the two resulting exhaust products, which varied substantially in composition. The particulate matter (PM) concentrations in the exhaust products were similar to those found in certain occupational and high ambient outdoor settings. Under partial load, the PM constituent had higher organic carbon, ammonium, sulfate, and nitrate mass, lower elemental (black) carbon mass, and smaller particle size, compared with full-load exhaust. Vapor phase partial-load exhaust had a greater mass of carbon monoxide and nonmethane volatile organic compounds, a higher percentage of naphthalenes, and a lower percentage of alkanes.

Using mice for their animal models, the researchers found that the exhaust byproducts from the two different engine loads resulted in very different health impacts. For example, the mice exposed to full-load exhaust had significantly more lung inflammation than those exposed to partial-load exhaust. The article notes a wide variety of different impacts depending on the type of exhaust to which the mice were exposed.

The researchers conclude that the typical practice of evaluating DEE health effects based solely on the PM mass concentration of the exhaust is misleading. Instead, they recommend that studies carefully analyze and describe the DEE compositions they use in their studies so different bodies of work can be more accurately compared.

The study can be found at http://ehp03.niehs.nih.gov/article/fetchArticle.action;jsessionid=C5C46D7253EFDD1EB0C56047334F9BC0?articleURI=info%3Adoi%2F10.1289%2Fehp.1003101.