Trainer Melissa G, Pavlov Alexander A, DeWitt H Langley, Jimenez Jose L, McKay Christopher P, Toon Owen B, Tolbert Margaret A
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309, USA.
Proc Natl Acad Sci U S A. 2006 Nov 28;103(48):18035-42. doi: 10.1073/pnas.0608561103. Epub 2006 Nov 13.
Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn's moon, Titan. One of Titan's most captivating features is the thick organic haze layer surrounding the moon, believed to be formed from photochemistry high in the CH(4)/N(2) atmosphere. It has been suggested that a similar haze layer may have formed on the early Earth. Here we report laboratory experiments that demonstrate the properties of haze likely to form through photochemistry on Titan and early Earth. We have used a deuterium lamp to initiate particle production in these simulated atmospheres from UV photolysis. Using a unique analysis technique, the aerosol mass spectrometer, we have studied the chemical composition, size, and shape of the particles produced as a function of initial trace gas composition. Our results show that the aerosols produced in the laboratory can serve as analogs for the observed haze in Titan's atmosphere. Experiments performed under possible conditions for early Earth suggest a significant optical depth of haze may have dominated the early Earth's atmosphere. Aerosol size measurements are presented, and implications for the haze layer properties are discussed. We estimate that aerosol production on the early Earth may have been on the order of 10(14) g.year(-1) and thus could have served as a primary source of organic material to the surface.
卡西尼号/惠更斯号探测器最近的探测激发了人们对土星卫星土卫六的极大兴趣。土卫六最引人入胜的特征之一是其周围厚厚的有机霾层，据信这是由甲烷/氮气大气层高处的光化学反应形成的。有人提出，早期地球上可能也形成了类似的霾层。在此，我们报告了实验室实验，这些实验展示了可能在土卫六和早期地球上通过光化学反应形成的霾的特性。我们使用氘灯通过紫外线光解在这些模拟大气中引发颗粒生成。利用一种独特的分析技术——气溶胶质谱仪，我们研究了所产生颗粒的化学成分、大小和形状随初始痕量气体成分的变化情况。我们的结果表明，实验室中产生的气溶胶可作为土卫六大气层中观测到的霾的类似物。在早期地球可能的条件下进行的实验表明，显著的霾光学厚度可能在早期地球大气层中占主导地位。本文给出了气溶胶大小测量结果，并讨论了其对霾层特性的影响。我们估计早期地球上气溶胶的生成量可能约为每年10¹⁴克，因此可能是向地表输送有机物质的主要来源。
