Nitrogen Stable Isotope Composition ( delta super( 15)N) of Vehicle-Emitted NO sub( x)

The nitrogen stable isotope ratio of NO... (...N-NO...) has been proposed as a regional indicator for NO... source partitioning; however, knowledge of ...N values from various NO... emission sources is limited. This study presents a detailed analysis of ...N-NO... emitted from vehicle exhaust, the largest source of anthropogenic NO... To accomplish this, NO... was collected from 26 different vehicles, including gasoline and diesel-powered engines, using a modification of a NO... collection method used by the United States Environmental Protection Agency, and ...N-NO... was analyzed. The vehicles sampled in this study emitted ...N-NO... values ranging from -19.1 to 9.8... that negatively correlated with the emitted NO... concentrations (8.5 to 286 ppm) and vehicle run time because of kinetic isotope fractionation effects associated with the catalytic reduction of NO... A model for determining the mass-weighted ...N-NO... from vehicle exhaust was constructed on the basis of average commute times, and the model estimates an average value of -2.5 plus or minus 1.5..., with slight regional variations. As technology improvements in catalytic converters reduce cold-start emissions in the future, it is likely to increase current ...N-NO... values emitted from vehicles. (ProQuest: ... denotes formulae/symbols omitted.)