Contribution of combustion Fe in marine aerosols over the northwestern Pacific estimated by Fe stable isotope ratios
Contribution of combustion Fe in marine aerosols over the northwestern Pacific estimated by Fe stable isotope ratios
复制标题
利用铁稳定同位素比值估算西北太平洋海洋气溶胶中燃烧源铁的贡献
DOI：
10.5194/acp-21-16027-2021
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发表时间：
2021-10-29
影响因子：
6.3
通讯作者：
Takahashi, Yoshio
中科院分区：
文献类型：
--
作者：
Kurisu, Minako;Sakata, Kohei;Takahashi, Yoshio
气溶胶铁（Fe）的来源解析是一个重要的问题，因为气溶胶铁可以促进海洋表层的初级生产，包括自然铁和燃烧铁。基于我们之前的发现，蒸发过程排放的燃烧铁的铁同位素比率（δ Fe-56）比天然铁的同位素比率低约千分之四，本研究旨在使用两种大小分馏的海洋气溶胶来区分西北太平洋上空的气溶胶铁源。来自东太平洋或北太平洋的细颗粒和粗颗粒的δ Fe-56值彼此相似，范围从千分之0.0到千分之0.4。其中大部分接近地壳平均水平，表明天然铁占主导地位。另一方面，来自东亚方向的颗粒在细颗粒中表现出较低的δ Fe-56值（-0.5 -2.2），而在粗颗粒中（平均-0.02 +/- 0.12）。δ Fe-56值与铅、钒富集因子的相关性表明，较低的δ Fe-56值是由于燃烧铁的存在所致。该区域细颗粒可溶组分的δ Fe-56值低于总Fe-56值，表明燃烧Fe优先溶解。此外，我们发现δ Fe-56值与来自东亚方向的气团中Fe溶解度分数呈负相关。这些结果表明，燃烧铁的存在是控制东亚方向气团中铁溶解度的重要因素，而其他因素在其他地区更为重要。通过假设燃烧和天然铁的典型δ Fe-56值，估计燃烧铁对气溶胶中总铁（酸消化）的贡献可达50%的细颗粒和21%的大块（粗+细）颗粒，而在其他地区其贡献很小。对一个样品估计，燃烧铁对可溶性铁组分的贡献约为总铁组分的两倍，表明燃烧铁作为可溶性铁源的重要性，尽管其排放量低于自然排放。将这些基于同位素的估算值与大气化学输送模型（IMPACT）的估算值进行了比较，其中细颗粒中燃烧铁的组分，特别是来自东亚方向的气团，彼此一致。相比之下，该模型估计粗颗粒中燃烧铁的贡献相对较大，这可能是因为模型计算和基于同位素的估算中包含了燃烧铁的不同特征。这突出了Fe-56的观测数据对于模型计算燃烧Fe排放的重要性。在东亚方向的气团中，燃烧和天然气溶胶对海洋表层的平均沉积通量分别为1.4和2.9 nmol m(-2) d(-1)，表明燃烧铁可能是海洋表层重要的铁源。利用海洋气溶胶和海水的δ Fe-56值来区分铁源，有望对大气和海洋表面的铁循环有更定量的了解。
The source apportionment of aerosol iron (Fe), including natural and combustion Fe, is an important issue because aerosol Fe can enhance oceanic primary production in the surface ocean. Based on our previous finding that combustion Fe emitted by evaporation processes has Fe isotope ratios (delta Fe-56) that are approximately 4 parts per thousand lower than those of natural Fe, this study aimed to distinguish aerosol Fe sources over the northwestern Pacific using two size-fractionated marine aerosols. The delta Fe-56 values of fine and coarse particles from the eastern or northern Pacific were found to be similar to each other, ranging from 0.0 parts per thousand to 0.4 parts per thousand. Most of them were close to the crustal average, suggesting the dominance of natural Fe. On the other hand, particles from the direction of East Asia demonstrated lower delta Fe-56 values in fine particles (-0.5 parts per thousand to -2.2 parts per thousand) than in coarse particles (on average -0.02 +/- 0.12 parts per thousand). The correlations between the delta Fe-56 values and the enrichment factors of lead and vanadium suggested that the low delta Fe-56 values obtained were due to the presence of combustion Fe. The delta Fe-56 values of the soluble component of fine particles in this region were lower than the total, indicating the preferential dissolution of combustion Fe. In addition, we found a negative correlation between the delta Fe-56 value and the fractional Fe solubility in air masses from the direction of East Asia. These results suggest that the presence of combustion Fe is an important factor in controlling the fractional Fe solubility in air masses from the direction of East Asia, whereas other factors are more important in the other areas. By assuming typical delta Fe-56 values for combustion and natural Fe, the contribution of combustion Fe to the total (acid-digested) Fe in aerosols was estimated to reach up to 50 % of fine and 21 % of bulk (coarse + fine) particles in air masses from the direction of East Asia, whereas its contribution was small in the other areas. The contribution of combustion Fe to the soluble Fe component estimated for one sample was approximately twice as large as the total, indicating the importance of combustion Fe as a soluble Fe source despite lower emissions than the natural. These isotope-based estimates were compared with those estimated using an atmospheric chemical transport model (IMPACT), in which the fractions of combustion Fe in fine particles, especially in air masses from the direction of East Asia, were consistent with each other. In contrast, the model estimated a relatively large contribution from combustion Fe in coarse particles, probably because of the different characteristics of combustion Fe that are included in the model calculation and the isotope-based estimation. This highlights the importance of observational data on delta Fe-56 for size-fractionated aerosols to scale the combustion Fe emission by the model. The average deposition fluxes of soluble Fe to the surface ocean were 1.4 and 2.9 nmol m(-2) d(-1) from combustion and natural aerosols, respectively, in air masses from the direction of East Asia, which suggests that combustion Fe could be an important Fe source to the surface seawater among other Fe sources.Distinguishing Fe sources using the delta Fe-56 values of marine aerosols and seawater is anticipated to lead to a more quantitative understanding of the Fe cycle in the atmosphere and surface ocean.