Isotopic Fractionation of Nitrous Oxide: Constraints on Its Biogenic Sources

一氧化二氮（N2 O）在控制平流层臭氧方面起着重要作用，并且是重要的温室气体。 一氧化二氮在大气中的含量不断增加，已成为《蒙特利尔议定书》规定的管制目标。 以前对平流层N2 O的稳定同位素测量表明，15/14 N和18/16 O比值高度富集。 有人提出，这种分馏是由各种同位素异构体的光解速率的变化引起的。 该项目涉及在198-220纳米波长范围内通过紫外光分解对N2 O同位素分馏进行实验室研究。 将在高光谱分辨率下测量各种一氧化二氮同位素的紫外吸收截面。还将利用质谱和近红外傅里叶变换光谱进行光解实验，以检查残留N2 O的同位素分馏。这些实验的结果将用于完善大气一氧化二氮同位素比率测量的解释，并提高我们对各种源和汇对全球大气一氧化二氮预算的贡献的理解。

Nitrous oxide (N2O) plays a significant role in terms of controlling stratospheric ozone and is an important greenhouse gas. N2O is increasing in the atmosphere and has been targeted for regulation under the Montreal Protocol. Previous stable isotopic measurements of stratospheric N2O have demonstrated highly enriched 15/14N and 18/16O ratios. It has been proposed that this fractionation is caused by variations in the photolysis rate of various isotopomers. This project involves the laboratory investigation of the isotopic fractionation of N2O by ultraviolet photolysis in the wavelength range 198-220 nm. The ultraviolet absorption cross sections of various nitrous oxide isotopomers will be measured at high spectral resolution. Photolysis experiments will also be carried out with mass spectrometric and near-infrared Fourier transform spectroscopy to examine the isotopic fractionation of residual N2O. The results of these experiments will be used to refine the interpretation of atmospheric nitrous oxide isotopic ratio measurements and improve our understanding of the contribution of various sources and sinks to the global atmospheric nitrous oxide budget.