Observational analysis demonstrates over 90% collection efficiency for atmospheric NOx in ambient air, indicating vehicle exhaust as the primary emission source.
The nitrogen isotopic composition of nitrogen oxide (NO x ) is useful for estimating its sources and sinks. Several methods have been developed to convert atmospheric nitric oxide (NO) and/or nitrogen dioxide (NO 2 ) to nitrites and/or nitrates for collection. However, the collection efficiency and blanks are poorly evaluated for many collection methods. Here, we present a method for collecting ambient NO x (NO and NO 2 simultaneously) with over 90% efficiency collection of NO x and low blank (approximately 0.5 μM) using a 3 wt% hydrogen peroxide (H 2 O 2 ) and 0.5 M sodium hydride (NaOH) solution. The 1σ uncertainty of the nitrogen isotopic composition was ± 1.2 ‰. The advantages of this method include its portability, simplicity, and the ability to collect the required amount of sample to analyze the nitrogen isotopic composition of ambient NO x in a short period of time. Using this method, we observed the nitrogen isotopic compositions of NO x at the Tsukuba and Yoyogi sites in Japan. The averaged δ 15 N(NO x ) value and standard deviation (1σ) in the Yoyogi site was (−2.7 ± 1.8) ‰ and in the Tsukuba site was (−1.7 ± 0.9) ‰ during the sampling period. The main NO x source appears to be the vehicle exhaust in the two sites.
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Kamezaki et al. (2024) studied this question.
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