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Abstract *
Diesel engines are a major source of underground miners' exposure to nitrogen dioxide. In an effort to reduce the exposure of underground miners to regulated and unregulated diesel emissions, primarily particulate matter, mining companies in the U.S. are retrofitting existing and introducing new engines with various exhaust aftertreatment technologies. Different aftertreatment devices, or changing the operating temperature of a selected device, can have unexpected effects on the concentration of nitrogen dioxide emitted by a diesel-powered piece of equipment. This paper provides an overview of the effects different exhaust aftertreatment technologies available to the mining industry have on NO2 emissions.
Introduction
Diesel engines are the major source of underground miners' exposure to nitric oxide (NO) and nitrogen dioxide (NO2). NO is a gas with a sharp, sweet smell; it is colorless to brown at room temperature. NO2 is also a colorless-tobrown gas at room temperature, but it has a strong, harsh odor. NO2 becomes reddish-brown at higher temperatures. NO and NO2 are eye, skin and respiratory tract irritants. NO and NO2 cause short-term (acute) and long-term (chronic) health problems, mostly pulmonary and cardiac related (Sunyer et al., 1997; Stieb et al., 2002). NO, is a potent oxidizer and can potentiafly interact with other pollutants and induce the formation of ozone (O,) and secondary hazardous particles (Peters et al., 1999; WHO, 2005).
The exposure of underground miners to NO and NO2 is regulated by the U.S. Mine Safety and Health Administration (MSHA). The enforced threshold limit values (TLV) for NO and NO2 are 25 ppm (time-weighted average, of TVA) and 5 ppm (ceiling), respectively, for both metal/nonmetal (MSHA, 1996) and underground coal mining (MSHA). The TLV ceiling limit is by definition the concentration that may not be exceeded for any length of time. It is important to note that MSHA used the American Conference of Government Industrial Hygienists' (ACGIH) 1972 (coal) and 1973 (metal and nonmetal) TLVs to set these standards (OSHA, 1988).
As engine exhaust emissions, NO and NO2 are generally referred to as nitrogen oxides (NOx) and, together with particulate matter, they represent the most difficult diesel engine emission products to control. The NOx emission rates are a function of a number of factors, such as engine design, engine operating conditions and...