【Objective】Nitrogen oxides (NO_x = NO and NO₂) are now a critical kind of trace component that calls for strict control, for they threaten the environment and human health. As NO_x has its unique isotope signature that varies with its source, the technique of stable isotope analysis can be used to investigate its origin and pathways. This study is to introduce a new method, chemical conversion process, for determination of ¹⁵N natural abundance (δ¹⁵N) of the nitrogen oxides from major anthropogenic sources. With the aid of this method, it is feasible for us to gradually understand the problem caused by NO_x emissions and hence to design appropriate relevant strategies to manage it.【Method】Based mainly on the technique of isotopic analysis of nitrous oxide (N₂O), the chemical conversion method is first to oxidize NO_x into nitrate (NO₃^-) with hydrogen peroxide (H₂O₂) in an acid condition. The resultant NO₃^- was then converted into N₂O under the joint effect of vanadium (III) chloride (VCl₃) and sodium azide (NaN₃) in a strong acid condition. The newly formed N₂O is trapped in an automatic cryogenic system and then diverted into a gas chromatographic column for analysis. The isolated nitrous oxide is analyzed in a stable isotope mass spectrometer under the continuous flowing mode for determination of δ¹⁵N, which is then converted into that of the initial NO_x using an equation. While testing this method, some other tests were carried out to optimize the experimental conditions for this method. After these tests, eventually NO_x in gas samples of different sources can be trapped completely in the absorption solution, with absorption rate reaching as high as 99%. At this time, fractionation of stable isotope is inhibited due to incomplete absorption. As conversion of NO_x into NO₃^- takes place in the absorption solution, it is possible to use standard nitrate solutions to simulate the absorption solutions that contained NO_x standard gas sample. Usgs32 and usgs34 are mixed at different volume ratios to prepare standard reference solutions different in stable isotope ratio. After the NO₃^- in these solutions is converted into N₂O using the above-described method and δ¹⁵N’s in the two are correlated one by one, a conversion curve between NO₃^- and N₂O in acquired. This curve is equal to the one between NO_x and N₂O in value. Along with increasing concentration of NO₃^- in the solution, the curve rises in gradient, tending towards 0.5 in theoretical value. This phenomenon appears as a result of blank in experiment. When the conversion curve is collated through blank correction, the phenomenon disappears and then gradient of the curve approaches 0.5, the theoretic value.【Result】Determination using this method may reach 0.09‰ in precision. Moreover, the minimal amount of a sample for the test is only 7 μg in terms of nitrogen. Gas samples from different sources, including vehicles and power plants, can be analyzed using this method. It is found that δ¹⁵N Air of the NO_x in vehicle exhaust is -3.6‰ on average, ranging from -17.4‰ to 4.0‰; and that in exhaust from power plants, 21.9‰, on average, ranging from 11.9‰ to 29.5‰, which are in good agreement with the findings in previous researches.【Conclusion】This method can be used for determining stable isotope ratio of NO_x from a variety of anthropogenic sources, including power plants and vehicles, and is good enough in precision and accuracy to meet the needs of the researches on NO_x.