Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA.
Proc Natl Acad Sci U S A. 2013 Feb 5;110(6):2035-40. doi: 10.1073/pnas.1212386110. Epub 2013 Jan 23.
Atmospheric iodine monoxide (IO) is a radical that catalytically destroys heat trapping ozone and reacts further to form aerosols. Here, we report the detection of IO in the tropical free troposphere (FT). We present vertical profiles from airborne measurements over the Pacific Ocean that show significant IO up to 9.5 km altitude and locate, on average, two-thirds of the total column above the marine boundary layer. IO was observed in both recent deep convective outflow and aged free tropospheric air, suggesting a widespread abundance in the FT over tropical oceans. Our vertical profile measurements imply that most of the IO signal detected by satellites over tropical oceans could originate in the FT, which has implications for our understanding of iodine sources. Surprisingly, the IO concentration remains elevated in a transition layer that is decoupled from the ocean surface. This elevated concentration aloft is difficult to reconcile with our current understanding of iodine lifetimes and may indicate heterogeneous recycling of iodine from aerosols back to the gas phase. Chemical model simulations reveal that the iodine-induced ozone loss occurs mostly above the marine boundary layer (34%), in the transition layer (40%) and FT (26%) and accounts for up to 20% of the overall tropospheric ozone loss rate in the upper FT. Our results suggest that the halogen-driven ozone loss in the FT is currently underestimated. More research is needed to quantify the widespread impact that iodine species of marine origin have on free tropospheric composition, chemistry, and climate.
大气中的碘一氧化物 (IO) 是一种自由基，它能催化破坏吸热臭氧，并进一步反应形成气溶胶。在这里，我们报告了在热带自由对流层 (FT) 中检测到 IO。我们展示了来自太平洋上空机载测量的垂直分布，显示高达 9.5 公里高度的显著 IO，并平均定位在海洋边界层以上的总柱的三分之二以上。在最近的深对流流出物和老化的自由对流层空气中都观察到了 IO，表明 FT 中热带海洋上广泛存在 IO。我们的垂直剖面测量结果表明，卫星在热带海洋上探测到的大部分 IO 信号可能源自 FT，这对我们理解碘源具有重要意义。令人惊讶的是，IO 浓度在与海洋表面解耦的过渡层中仍然升高。这种高空升高的浓度与我们目前对碘寿命的理解很难协调一致，可能表明从气溶胶到气相的碘异相再循环。化学模式模拟表明，碘引起的臭氧损耗主要发生在海洋边界层以上（34%）、过渡层（40%）和 FT（26%），占 FT 上部总大气臭氧损耗率的 20%。我们的研究结果表明，FT 中的卤驱动臭氧损耗目前被低估了。需要进一步研究以量化海洋起源的碘物质对自由对流层成分、化学和气候的广泛影响。
