A fuel-based assessment of off-road diesel engine emissions

The use of diesel engines in off-road applications is a significant source of nitrogen oxides (NOx) and particulate matter (PM10). Such off-road appli cations include railroad locomotives, marine vessels, and equipment used fo r agriculture, construction, logging, and mining. Emissions from these sour ces are only beginning to be controlled. Due to the large number of these e ngines and their wide range of applications, total activity and emissions f rom these sources are uncertain. A method for estimating the emissions from off-road diesel engines based on the quantity of diesel fuel consumed is p resented. Emission factors are normalized by fuel consumption, and total ac tivity is estimated by the total fuel consumed. Total exhaust emissions from off-road diesel equipment (excluding locomotiv es and marine vessels) in the United States during 1996 have been estimated to be 1.2 x 10(9) kg NOx and 1.2 x 10(8) kg PM10. Emissions estimates publ ished by the U.S. Environmental Protection Agency are 2.3 times higher for both NOx and exhaust PM,, emissions than estimates based directly on fuel c onsumption. These emissions estimates disagree mainly due to differences in activity estimates, rather than to differences in the emission factors. Al l current emission inventories for off-road engines are uncertain because o f the limited in-use emissions testing that has been performed on these eng ines. Regional- and state-level breakdowns in diesel fuel consumption by of f-road mobile sources are also presented. Taken together with on-road measu rements of diesel engine emissions, results of this study suggest that in 1 996, off-road diesel equipment (including agriculture, construction, loggin g, and mining equipment, but not locomotives or marine vessels) was respons ible for 10% of mobile source NOx emissions nationally, whereas on-road die sel vehicles contributed 33%.