Interhemispheric asymmetry in OH abundance inferred from measurements of atmospheric 14CO
Interhemispheric asymmetry in OH abundance inferred from measurements of atmospheric 14CO
复制标题
根据大气 14CO 测量推断半球间 OH 丰度不对称
作者：
C. Brenninkmeijer;M. Manning;D. Lowe;G. Wallace;R. Sparks;A. Volz
羟基自由基是大气中的主要氧化剂，负责去除许多天然和人为的微量气体1。目前，不能在全球大气化学模型所需的空间和时间尺度上以足够的精度直接测量OH。因此，对大气中氢氧化氢丰度的估计依赖于将氢氧化氢化学和对氢氧化氢敏感的微量气体的观测相结合的模型。14CO是OH丰度3-6的重要诊断指标。它主要是在大气中由宇宙辐射产生的14C立即氧化产生的，随后通过羟基自由基氧化成14CO2的速度较慢。夏季中低纬地区清洁空气中~(14)CO的平均寿命约为一个月，这使得~(14)CO成为比通常使用的寿命更长的痕量气体更灵敏的氢氧化物指示剂。到目前为止，只有几个北半球的~(14)CO测定结果公布了3，8。利用加速器质谱仪，我们给出了新西兰的一组广泛的~(14)CO数据和几个新的北半球结果。我们发现，南半球的14CO浓度比北半球可比纬度的∼低40%。如此大的差异令人惊讶，因为人们认为两个半球的主要源和汇是相似的。尽管有几个复杂的因素，但我们的结果表明，与使用当前光化学模型预测的情况相反，南半球的OH丰度可能显著高于北半球。
THE hydroxyl radical, OH, is the chief oxidizing agent in the atmosphere, and is responsible for removing many natural and anthropogenic trace gases1. At present, OH cannot be measured directly with sufficient accuracy over the spatial and temporal scales needed for global models of atmospheric chemistry2. Consequently, estimates of atmospheric OH abundance rely on a combination of models incorporating OH chemistry and observations of trace gases sensitive to OH. 14CO is an important diagnostic of OH abundance3–6. It is produced in the atmosphere mainly by the immediate oxidation of 14C produced by cosmic radiation, and it is subsequently removed more slowly through oxidation to 14CO2 by hydroxyl radicals7. The mean lifetime of14CO in clean air during summer in the middle and low latitudes is about one month, which makes 14CO a more sensitive indicator of OH than the longer-lived trace gases commonly used. Until now, only a few Northern Hemisphere 14CO determinations have been published3,8. Using accelerator mass spectrometry we present here an extensive set of 14CO data in New Zealand and several new Northern Hemisphere results. We find that Southern Hemisphere14CO concentrations are ∼40% lower than at comparable latitudes in the Northern Hemisphere. Such a large difference is surprising because the dominant sources and sinks are believed to be similar in both hemispheres. Although there are several complicating factors, from our results we suggest that OH abundances may be significantly higher in the Southern Hemisphere than in the Northern Hemisphere, in contrast to predictions using current photochemical models.