Ugelow Melissa S, Berry Jennifer L, Browne Eleanor C, Tolbert Margaret A
Department of Chemistry, University of Colorado, Boulder, Colorado.
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado.
Astrobiology. 2020 May;20(5):658-669. doi: 10.1089/ast.2019.2145. Epub 2020 Mar 10.
Atmospheric organic hazes are common in planetary bodies in our solar system and likely exoplanet atmospheres as well. In addition, geochemical data support the existence of an organic haze in the early Earth's atmosphere. Much of what is known about organic haze formation derives from studies of Saturn's moon Titan. It is believed that on Titan ions play an important role in haze formation. It is possible, by using Titan as an analog for the Archean Earth, to consider that an Archean haze could have formed by similar processes. Here, we examine the anion chemistry that occurs during laboratory simulations of early Earth haze formation and measure the composition of gaseous anions as a function of O mixing ratio. Gaseous anion composition and relative abundances are measured by an atmospheric pressure interface time-of-flight mass spectrometer and are compared to previous photochemical haze mass loading measurements. Numerous anions are observed spanning from mass-to-charge ratio 26 to 246, with a majority of the identified anions containing carbon, hydrogen, nitrogen, and/or oxygen. A shift in the anion composition occurs with increasing the precursor O mixing ratio. With 0-20 ppmv O in CH/CO/N mixtures, ions contain mostly organic nitrogen, with CNO being the most intense ion peak. As the precursor O is increased to 200 and 2000 ppmv, inorganic nitrogen ions become the dominant chemical group, with NO having the most intense ion signal. The clear shift in the ionic composition could be indicative of a modification to the gas-phase chemistry that occurs in the transition from an anoxic atmosphere to an oxygen-containing atmosphere, with potential astrobiological significance.
大气有机霾在我们太阳系的行星体中很常见，在系外行星大气中可能也存在。此外，地球化学数据支持早期地球大气中存在有机霾。目前关于有机霾形成的许多认识都源于对土星卫星泰坦的研究。据信在泰坦上，离子在霾的形成中起重要作用。通过将泰坦作为太古宙地球的类比，可以认为太古宙霾可能是由类似过程形成的。在这里，我们研究了早期地球霾形成的实验室模拟过程中发生的阴离子化学，并测量了气态阴离子的组成随氧气混合比的变化。气态阴离子的组成和相对丰度通过大气压接口飞行时间质谱仪进行测量，并与之前的光化学霾质量负荷测量结果进行比较。观察到许多阴离子，质荷比范围从26到246，大多数已识别的阴离子含有碳、氢、氮和/或氧。随着前驱体氧气混合比的增加，阴离子组成发生变化。在CH/CO/N混合物中氧气含量为0 - 20 ppmv时，离子主要含有有机氮，CNO是最强的离子峰。当前驱体氧气增加到200和2000 ppmv时，无机氮离子成为主要化学基团，NO具有最强的离子信号。离子组成的明显变化可能表明在从缺氧大气向含氧大气转变过程中发生的气相化学变化，具有潜在的天体生物学意义。
