Department of Chemistry, University of Colorado Boulder, Boulder, CO 80309.
Cooperative Institute for Research in Environmental Sciences, Boulder, CO 80309.
Proc Natl Acad Sci U S A. 2020 Jan 28;117(4):1860-1866. doi: 10.1073/pnas.1916828117. Epub 2020 Jan 13.
Oceanic emissions of iodine destroy ozone, modify oxidative capacity, and can form new particles in the troposphere. However, the impact of iodine in the stratosphere is highly uncertain due to the lack of previous quantitative measurements. Here, we report quantitative measurements of iodine monoxide radicals and particulate iodine (I) from aircraft in the stratosphere. These measurements support that 0.77 ± 0.10 parts per trillion by volume (pptv) total inorganic iodine (I) is injected to the stratosphere. These high I amounts are indicative of active iodine recycling on ice in the upper troposphere (UT), support the upper end of recent I estimates (0 to 0.8 pptv) by the World Meteorological Organization, and are incompatible with zero stratospheric iodine injection. Gas-phase iodine (I) in the UT (0.67 ± 0.09 pptv) converts to I sharply near the tropopause. In the stratosphere, IO radicals remain detectable (0.06 ± 0.03 pptv), indicating persistent I recycling back to I as a result of active multiphase chemistry. At the observed levels, iodine is responsible for 32% of the halogen-induced ozone loss (bromine 40%, chlorine 28%), due primarily to previously unconsidered heterogeneous chemistry. Anthropogenic (pollution) ozone has increased iodine emissions since preindustrial times (ca. factor of 3 since 1950) and could be partly responsible for the continued decrease of ozone in the lower stratosphere. Increasing iodine emissions have implications for ozone radiative forcing and possibly new particle formation near the tropopause.
海洋排放的碘会破坏臭氧、改变氧化能力，并在对流层中形成新的颗粒。然而，由于缺乏先前的定量测量，平流层中碘的影响仍高度不确定。在此，我们报告了飞机在平流层中对碘一氧化物自由基和颗粒碘（I）的定量测量。这些测量结果表明，体积比为 0.77 ± 0.10 万亿分率（pptv）的总无机碘（I）被注入平流层。如此大量的 I 表明在上对流层（UT）的冰上存在活跃的碘循环，支持世界气象组织（WMO）最近对碘的估计值（0 至 0.8 pptv）的上限，且与平流层中零碘注入不相符。UT 中的气相碘（I）（0.67 ± 0.09 pptv）在对流层顶附近迅速转化为 I。在平流层中，IO 自由基仍可检测到（0.06 ± 0.03 pptv），这表明由于多相化学的活跃作用，I 持续循环回到 I。在观察到的水平下，碘负责 32%的卤化物诱导臭氧损耗（溴 40%，氯 28%），这主要是由于以前未考虑到的非均相化学。自工业化时代以来，人为（污染）臭氧增加了碘的排放（自 1950 年以来约增加了 3 倍），这可能是平流层下部臭氧持续减少的部分原因。碘排放的增加对臭氧辐射强迫以及对流层顶附近可能的新粒子形成有影响。
