title: Nitrogen stable isotope composition (δ15N) of vehicle-emitted NOx.
abstract: The nitrogen stable isotope ratio of NOx (δ(15)N-NOx) has been proposed as a regional indicator for NOx source partitioning; however, knowledge of δ(15)N values from various NOx emission sources is limited. This study presents a detailed analysis of δ(15)N-NOx emitted from vehicle exhaust, the largest source of anthropogenic NOx. To accomplish this, NOx was collected from 26 different vehicles, including gasoline and diesel-powered engines, using a modification of a NOx collection method used by the United States Environmental Protection Agency, and δ(15)N-NOx was analyzed. The vehicles sampled in this study emitted δ(15)N-NOx values ranging from -19.1 to 9.8‰ that negatively correlated with the emitted NOx concentrations (8.5 to 286 ppm) and vehicle run time because of kinetic isotope fractionation effects associated with the catalytic reduction of NOx. A model for determining the mass-weighted δ(15)N-NOx from vehicle exhaust was constructed on the basis of average commute times, and the model estimates an average value of -2.5 ± 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 δ(15)N-NOx values emitted from vehicles.
authors.affiliation: Department of Earth, Atmospheric, and Planetary Sciences and ‡Department of Chemistry, Purdue University , 550 Stadium Mall Drive, West Lafayette, Indiana 47907, United States.
authors.forename: Wendell W
authors.initials: WW
authors.lastname: Walters
authors.forename: Stanford R
authors.initials: SR
authors.lastname: Goodwin
authors.forename: Greg
authors.initials: G
authors.lastname: Michalski
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001336:Automobiles; D004784:Environmental Monitoring; D005742:Gasoline; D009587:Nitrogen Isotopes / Q000032:analysis*; D009589:Nitrogen Oxides / Q000032:analysis*; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D005742:Gasoline; D009587:Nitrogen Isotopes; D009589:Nitrogen Oxides; D001335:Vehicle Emissions