Experimental Study on Growth of Organic Aerosol in Reducing Planetary Atmospheres
Experimental Study on Growth of Organic Aerosol in Reducing Planetary Atmospheres
复制标题
还原行星大气中有机气溶胶生长的实验研究
DOI：
10.11203/jar.31.185
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
杉田精司
中科院分区：
文献类型：
--
作者：
洪鵬;関根康人;杉田精司
观测到的有机气溶胶层可能形成于含CH4的还原行星大气中。在土卫六的大气中，主要由氮气和甲烷组成，有机气溶胶是通过太阳紫外线驱动的光化学反应产生的。这种有机气溶胶可能存在于早期地球和系外行星的CH4-CO2大气中。由于甲烷大气中的气溶胶层控制着大气结构和地表温度，其形成机制对行星大气的演化具有重要意义。尽管卡西尼号航天器揭示了气溶胶粒子最初是通过极端紫外线照射在土卫六的上层大气中形成的，但在中层大气降水过程中气溶胶粒子的生长机制仍然受到很少的限制。在这里，我们进行了光化学反应和多相反应的实验室实验，以限制含甲烷大气中气溶胶的生长机制。实验和光化学模拟结果表明，土卫六中层大气中CH4光解生成的CH3自由基的加成反应是气溶胶粒子生长的主要过程。这一反应将通过增加有机气溶胶的数量和减少C2H6的数量来影响土卫六上的碳收支和碳循环。
Organic aerosol layers have been observed and suggested to form in CH 4-containing reducing planetary atmospheres. In Titan’s atmosphere, composed mainly of N 2 and CH 4, organic aerosols are produced through photochemical reactions driven by solar ultraviolet light. Such organic aerosols may have existed in the CH 4-CO 2 atmosphere of early Earth and exoplanets. Since the aerosol layers in CH 4-containing atmospheres control the atmospheric structure and surface temperature, their formation mechanisms are important for the evolution of planetary atmospheres. Although the Cassini spacecraft has revealed that aerosol particles are initially formed in Titan’s upper atmosphere by irradiation of extreme ultraviolet light, the growth mechanisms of aerosol particles during precipitation in the middle atmosphere remain poorly constrained. Here, we conduct laboratory experiments on photochemical and heterogeneous reactions to constrain the aerosol growth mechanisms in CH 4-containing atmospheres. Our results of the experiments and photochemical modeling suggest that the addition reaction of CH 3 radicals formed by CH 4 photolysis is the major process for the growth of aerosol particles in the middle atmosphere of Titan. This reaction would affect the carbon budget and cycles on Titan, through increasing the amounts of organic aerosols and reducing the amounts of C 2 H 6.