Minor effect of physical size sorting on iron solubility of transported mineral dust
Minor effect of physical size sorting on iron solubility of transported mineral dust
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DOI：
10.5194/acp-11-8459-2011
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发表时间：
2011-08
影响因子：
6.3
通讯作者：
Zongbo Shi;M. Woodhouse;K. Carslaw;M. Krom;G. Mann;A. Baker;I. Savov;G. Fones;B. Brooks;N. Drake;T. Jickells;L. Benning
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作者：
Zongbo Shi;M. Woodhouse;K. Carslaw;M. Krom;G. Mann;A. Baker;I. Savov;G. Fones;B. Brooks;N. Drake;T. Jickells;L. Benning
抽象的。观测结果表明，沙尘气溶胶中Fe的溶解度分数（FS-Fe，溶解态Fe占总Fe的百分比）从沙尘质量浓度高的地区的0.1%增加到浓度低的偏远地区的80%。在这里，我们结合实验室地球化学测量与全球气溶胶模型模拟来检验这一假设，即FS-Fe的增加是由于运输过程中的物理尺寸分选。我们确定了FS-Fe和分数溶解度的Al（FS-Al）的粒度分级粉尘中产生的两个代表性的土壤样品收集从已知的撒哈拉沙尘源区使用定制的灰尘再悬浮和收集系统。结果表明，FS-Fe是尺寸依赖性的，并且范围从粗尺寸级分（>1 μm）中的0.1- 0.3%到细尺寸级分（100 μg m-3）中的~0.2- 0.8%到低浓度（~ 3）下的~ 0.2%，这是由于物理尺寸分选（即，颗粒重力沉降）。这些数值比在撒哈拉尘埃羽流的一个重要路径下穿越热带和亚热带北大西洋的巡航观测到的数值小一到两个数量级，尘埃质量浓度相似。即使模型中亚微米粒级（0.18-0.32 μm、0.32-0.56 μm和0.56-1.0 μm）的FS-Fe比测量值增加10倍，计算的粉尘FS-Fe仍然比现场测量值低一个数量级以上。因此，单独的物理分选的灰尘颗粒是不太可能是一个重要的因素，在所观察到的FS-Fe和FS-Al和大气矿物粉尘质量浓度之间的反比关系。结果表明，化学反应和/或与燃烧颗粒物的混合等过程是导致远距离输送沙尘气溶胶中FS-Fe增加的主要机制。
Abstract. Observations show that the fractional solubility of Fe (FS-Fe, percentage of dissolved to total Fe) in dust aerosol increases considerably from 0.1 % in regions of high dust mass concentration to 80 % in remote regions where concentrations are low. Here, we combined laboratory geochemical measurements with global aerosol model simulations to test the hypothesis that the increase in FS-Fe is due to physical size sorting during transport. We determined the FS-Fe and fractional solubility of Al (FS-Al) in size-fractionated dust generated from two representative soil samples collected from known Saharan dust source regions using a customized dust re-suspension and collection system. The results show that the FS-Fe is size-dependent and ranges from 0.1–0.3 % in the coarse size fractions (>1 μm) to ~0.2–0.8 % in the fine size fractions ( 100 μg m −3 ) to ~0.2 % at low concentrations ( –3 ) due to physical size sorting (i.e., particle gravitational settling). These values are one to two orders of magnitude smaller than those observed on cruises across the tropical and sub-tropical North Atlantic Ocean under an important pathway of Saharan dust plumes for similar dust mass concentrations. Even when the FS-Fe of sub-micrometer size fractions (0.18–0.32 μm, 0.32–0.56 μm, and 0.56–1.0 μm) in the model is increased by a factor of 10 over the measured values, the calculated FS-Fe of the dust is still more than an order of magnitude lower than that measured in the field. Therefore, the physical sorting of dust particles alone is unlikely to be an important factor in the observed inverse relationship between the FS-Fe and FS-Al and the atmospheric mineral dust mass concentrations. The results suggest that processes such as chemical reactions and/or mixing with combustion particles are the main mechanisms to cause the increased FS-Fe in long-range transported dust aerosols.