Low blank sampling method for measurement of the nitrogen isotopic composition of atmospheric NO.sub.x

The nitrogen isotopic composition of nitrogen oxide (NO.sub.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.sub.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.sub.x (NO and NO.sub.2 simultaneously) with over 90% efficiency collection of NO.sub.x and low blank (approximately 0.5 [mu]M) using a 3 wt% hydrogen peroxide (H.sub.2 O.sub.2) and 0.5 M sodium hydride (NaOH) solution. The 1[sigma] 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.sub.x in a short period of time. Using this method, we observed the nitrogen isotopic compositions of NO.sub.x at the Tsukuba and Yoyogi sites in Japan. The averaged [delta].sup.15 N(NO.sub.x) value and standard deviation (1[sigma]) 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.sub.x source appears to be the vehicle exhaust in the two sites.