The overall objective of the research project was to ensure that no new health hazards were introduced into the underground mine environment by the use of modern, electronically controlled, low emission diesel engine technology. This was accomplished by evaluating the effects these diesel engines (operated with low sulfur fuel) on the mass concentration, chemical composition and physical characteristics of diesel particulate matter (DPM) in a domal salt mine. The study was modeled after previous studies in which the mass concentration, chemical composition and physical characteristics of DPM - were determined before and after the introduction of exhaust aftertreatment or alternative fuel to evaluate their effectiveness in reducing mass emissions. Sampling was conducted over a two-week period at several locations within the mine. The same protocol was followed during each week, except different diesel-powered vehicles were used. During the first week, 1990 Caterpillar 3408 C, mechanically controlled engines were used; during the second week, 1998 Caterpillar 3408 F, electronically controlled engines were used. The same low sulfur (34.2 ppm) fuel was used throughout the study. A variety of samples were collected to determine control efficiency and to determine the changes in the biological, chemical, and physical nature of the diesel aerosol attributable to the use of low-emission engines. DPM concentrations were determined using elemental carbon (EC) and size selective (SS) sampling techniques. The EC technique also provided information on total carbon (TC) and organic carbon (OC) levels. The SS technique provided information on respirable dust (RD) and <0.8 m particle concentrations. Several near real-time instruments were used for monitoring the diesel aerosol in the mine, i.e., portable diffusion chargers (DC) for total surface area, portable photoelectric aerosol sensors (PAS) for total surface-bound polycyclic aromatic hydrocarbons (PAH), and condensation particle counters (CPC) for particle numbers. High-volume samplers were used to obtain DPM samples for determination of the specific PAH and mutagenic activity associated with the adsorbed organics. In areas where the diesels were operating, the TC and EC were reduced by at least 60% with use of the electronically controlled diesel engines. OC levels were also reduced but to a lesser extent, consistent with the engine's technology changes affecting the EC component of the DPM. As determined from the SS samples, the reductions in DPM at the downwind location were not as great as for the TC (about 40% decreases in <0.8 m particles and RD). As determined in this mine, the DPM levels with the moden engines (and no control devices) would not reach the target value of 0.15 mg/m3. The EC and SS sampling methods were both found to work well in an underground mine environment. All of the near real-time aerosol measurements at the downwind location (DC, PAS, and CPC) showed about 50 to 60% decrease in levels with use of the late model engines. The magnitude of the decreases was similar to that found for EC and TC at the same locations, indicating that these parameters have close correlations. There was also no evidence of increased production of nano- (or nuclei-mode) particles with use of the late model engines. This study also demonstrated that instruments such as the DC, PAS and CPC can be used to track diesel activity on a real time basis in underground mines. The PAR and biological (mutagenic) activity levels (associated with the organics extracted from DPM collected with the high-volume samplers) also showed large decreases with use of the electronically controlled diesel engines (by up to about 90% and 65%, respectively). Overall, use of electronically controlled, modem diesel engines with a low sulfur fuel in this underground mine resulted in large reductions in DPM and all DPM-related components. The measured potentially health related components showed similar reductions. However, the use of these engines cannot be relied upon to reduce concentrations below 0.15 mg/m3 in all circumstances.
Department of Biological Sciences, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49930-1295