Design, characterization, and evaluation of a small-scale diesel exhaust exposure system

A single-cylinder engine diesel exhaust exposure system was constructed to conduct laboratory health effects studies. The single-cylinder engine was selected to provide a cost-effective and easy-to-operate biological exposure system as an alternative to larger engines operated on chassis or test stand dynamometers. The engine was a 5500-watt diesel generator operated at load by connection to a bank of 11 500 watt light sources. The engine was isolated from the rodent and cell exposure chambers to ameliorate excessive noise and heat in the exposure room. Exhaust was diluted approximately 100: 1 and routed to a 1 m(3) flow-through exposure chamber where the exhaust composition was assessed in detail. Measurements included particle mass, particle size distribution ( based on both number and mass), carbon monoxide, nitrogen oxides, particle carbon ( organic and elemental), particle sulfate/nitrate, metals, total and speciated volatile hydrocarbons, and speciated semivolatile and particle-phase polycyclic aromatic hydrocarbons. The exhaust composition was compared with published diesel exhaust compositions and that from a 2000 Model Cummins 5.9L ISB engine, which was operated on a variable duty cycle on a dynamometer using the same fuel and lube oil as the single-cylinder engine. The exhaust composition from the single-cylinder engine was consistent with "typical" diesel exhaust and the larger on-road engine. It yielded particle mass with a mass median diameter of similar to 0.1 mum that was composed of similar to70% elemental carbon, similar to35% organic carbon,similar to 4-5% sulfate/nitrate, and small amounts of metals. The volatile and speciated organic/inorganic gases were in the range of literature values, with specific characteristics of low particle bound aromatic compounds and higher amounts of volatile and oxygenated organics. Based on this evaluation, the single-cylinder engine and exhaust dilution system described here generates emissions that should be useful for studying health hazards that pertain to emissions from a broad range of diesel engines.