Diesel Exhaust: Methods for Measuring

Because diesel fuel exhaust is composed of thousands of different chemicals, measuring the concentration and composition of the exhaust is extremely difficult. The analysis of DE is further complicated by the fact that the compounds within exhaust react with each other forming successively larger and more complex chemicals. Diesel particulate matter can be created initially from the combustion (as carbonaceous compounds) or can be from a secondary source (transformation and condensation of gaseous products). Another factor making measurement complicated is the dilution factor. In a truck traveling down the freeway at 60mph, measuring the amount of DPM is dependant upon how easily it is dispersed into the atmosphere. Finally, determining the composition of diesel fuel exhaust is difficult because of the fact that all components have different half lives in the atmosphere, and many change form within seconds of emission from the diesel engine. For a thorough summary of DPM problems in measurement, see appendix of the ToxProbe document (2002): http://www.city.toronto.on.ca/health/pdf/de_technical_11.pdf

In the environment, the most common method of measuring DPM is through gravimetric analysis. An instrument with a quartz filter is used near an emission source. The filter is allowed to collect exhaust for a specified time and is then analyzed to determine the total mass of the particulate matter.

Another instrument, the Electrical Aerosol Analyzer uses an electron beam to positively charge the exhaust particles to create size distribution data. The Photoelectric Aerosol Sensor is used specifically to measure the quantity of PAH emitted.

Problems in these measurements are caused by difficulty in the real-time collection and interpretation of data, as well as control of interferences in the atmosphere.

“Which instrument is used is dependent on the particle sizes and characteristics of interest, the goals of the study, and the respective limitations of each instrument” (Kittelson et. al., p. 27, 1999)

The University of Minnesota Center for Diesel Research published a comprehensive review of commonly used instruments for measuring diesel exhaust contents and concentrations. “Review of diesel particulate matter sampling methods final report” D. Kittelson, M. Arnold and W. Watts Jr. January 14, 1999. http://www.me.umn.edu/centers/cdr/reports/EPAreport3.pdf

Methods for measuring levels of diesel particulate matter in humans has been a challenge on many fronts. A serious sampling problem that needs to be addressed is that of controlling for cigarette smoke. The use of biomarkers to study levels of diesel exhaust absorbed into the body began in the 1990’s. One study focused on the presence of DNA adducts (conglomerations and branching) in the lymphocytes and blood cells of bus garage workers. Other studies have investigated the presence of 1-hydroxypyrene, a by-product of PAH in urine. See the EPA’s final health assessment for further details: http://oaspub.epa.gov/eims/eimscomm.getfile?p_download_ id=36255

Studies on DE affects on rats have been completed and permissible exposure limits (PEL) have been determined by OSHA through extrapolation, but many questions remain. “How does diesel particulate matter cause a tumorgenic response?” “What are the components of DE and which are most likely to cause problems in humans?” “Where do diesel exhaust by-products go in the environment and what kind of harm can they cause?”

Until measuring diesel exhaust compounds becomes a more accurate and reliable option, these questions will remain.