A revised global ozone dry deposition estimate based on a new two-layer parameterisation for air–sea exchange and the multi-year MACC composition reanalysis
A revised global ozone dry deposition estimate based on a new two-layer parameterisation for air–sea exchange and the multi-year MACC composition reanalysis
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DOI：
10.5194/acp-18-4329-2018
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发表时间：
2018-03
影响因子：
6.3
通讯作者：
A. Luhar;M. Woodhouse;I. Galbally
中科院分区：
文献类型：
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作者：
A. Luhar;M. Woodhouse;I. Galbally
抽象的。地球表面的干沉积是大气臭氧的重要汇。目前，与其他表面类型的沉积相比，大气化学模型中臭氧向海洋表面的干沉积具有最大的不确定性，这对全球对流层臭氧预算和相关辐射强迫具有影响。大多数全球模型假设海洋表面臭氧干沉降速度参数化中表面阻力的主导项是恒定的。最近有气海交换的机械参数化，可以解释臭氧溶解度、分子扩散、湍流传递以及臭氧与溶解的碘化物和其他化合物的一级化学反应的同步水侧过程，但它们的性能和一致性存在问题。我们通过做出以下实际假设，提出了一种新的海洋表面阻力两层参数化方案：（a）顶层水层的厚度为反应扩散长度尺度（几微米），其中臭氧损失主要由化学反应主导，水侧湍流传递的影响可以忽略不计； (b) 在下面的水层中，化学反应和水侧湍流传递共同作用并被考虑； (c) 化学反应性贯穿海洋混合层的深处。新的参数化已经根据最近的公海测量的干沉积速度进行了评估。结果发现，仅包含碘化物水溶液-臭氧反应即可令人满意地描述测量结果。为了更好地量化全球干沉降损失及其年际变化，将 2003-2012 年 3 小时臭氧沉降速度模型与 3 小时 MACC（监测大气成分和气候）再分析臭氧相结合。结果发现，海洋臭氧干沉降量为 98.4 ± 30.0 Tg O3 yr−1，全球臭氧干沉降量为 722.8 ± 87.3 Tg O3 yr−1。海洋成分的新估计大约是当前模型估计的三分之一。这一减少相当于全球臭氧干沉降总量减少约 20%，这（所有其他成分不变）相当于模拟的对流层臭氧负荷增加约 5%，对流层臭氧寿命也有类似的增加。
Abstract. Dry deposition at the Earth's surface is an important sink of atmospheric ozone. Currently, dry deposition of ozone to the ocean surface in atmospheric chemistry models has the largest uncertainty compared to deposition to other surface types, with implications for global tropospheric ozone budget and associated radiative forcing. Most global models assume that the dominant term of surface resistance in the parameterisation of ozone dry deposition velocity at the oceanic surface is constant. There have been recent mechanistic parameterisations for air–sea exchange that account for the simultaneous waterside processes of ozone solubility, molecular diffusion, turbulent transfer, and first-order chemical reaction of ozone with dissolved iodide and other compounds, but there are questions about their performance and consistency. We present a new two-layer parameterisation scheme for the oceanic surface resistance by making the following realistic assumptions: (a) the thickness of the top water layer is of the order of a reaction–diffusion length scale (a few micrometres) within which ozone loss is dominated by chemical reaction and the influence of waterside turbulent transfer is negligible; (b) in the water layer below, both chemical reaction and waterside turbulent transfer act together and are accounted for; and (c) chemical reactivity is present through the depth of the oceanic mixing layer. The new parameterisation has been evaluated against dry deposition velocities from recent open-ocean measurements. It is found that the inclusion of only the aqueous iodide–ozone reaction satisfactorily describes the measurements. In order to better quantify the global dry deposition loss and its interannual variability, modelled 3-hourly ozone deposition velocities are combined with the 3-hourly MACC (Monitoring Atmospheric Composition and Climate) reanalysis ozone for the years 2003–2012. The resulting ozone dry deposition is found to be 98.4 ± 30.0 Tg O3 yr−1 for the ocean and 722.8 ± 87.3 Tg O3 yr−1 globally. The new estimate of the ocean component is approximately a third of the current model estimates. This reduction corresponds to an approximately 20 % decrease in the total global ozone dry deposition, which (with all other components being unchanged) is equivalent to an increase of approximately 5 % in the modelled tropospheric ozone burden and a similar increase in tropospheric ozone lifetime.