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Iron dissolution kinetics of mineral dust at low pH during simulated atmospheric processing

机译：模拟大气处理过程中低pH下矿物粉尘的铁溶解动力学

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摘要

We investigated the iron (Fe) dissolution kinetics of African (Tibesti) and Asian (Beijing) dust samples at acidic pH with the aim of reproducing the low pH conditions in atmospheric aerosols. The Beijing dust and three size fractions of the Tibesti dust (<20 μm: PM20; <10 μm: PM 10; and <2.5 μm: PM2.5) were dissolved at pH 1, 2 and/or 3 for up to 1000 h. In the first 10 min, all dust samples underwent an extremely fast Fe solubilisation. Subsequently, the Fe dissolution proceeded at a much slower rate before reaching a stable dissolution plateau. The time-dependant Fe dissolution datasets were best described by a model comprising three acid-extractable Fe pools each dissolving according to first-order kinetics. The dissolution rate constant k (h~(-1)) of each pool was independent of the source (Saharan or Asian) and the size (PM20, PM10 or PM_(2.5)) of the dust but highly dependent on pH. The "fast" Fe pool had a k (25 h-1 at pH Combining double low line 1) of a similar magnitude to "dry" ferrihydrite nanoparticles and/or poorly crystalline Fe(III) oxyhydroxide, while the " intermediate" and "slow" Fe pools had k values respectively 50-60 times and 3000-4000 times smaller than the "fast" pool. The "slow" Fe pool was likely to consist of both crystalline Fe oxide phases (i.e., goethite and/or hematite) and Fe contained in the clay minerals. The initial mass of the "fast", "intermediate" and "slow" Fe pools represented respectively about 0.5-2%, 1-3% and 15??"40% of the total Fe in the dust samples. Furthermore, we showed that in systems with low dust/liquid ratios, Fe can be dissolved from all three pools, whereas at high dust/liquid ratios (e.g., in aerosols), sufficient Fe may be solubilised from the "fast" phase to dominate the Fe dissolved and to suppress the dissolution of Fe from the other Fe pools. These data demonstrated that dust/liquid ratio and pH are fundamental parameters controlling Fe dissolution kinetics in the dust. In order to reduce errors in atmospheric and climate models, these fundamental controlling factors need to be included.
机译：我们研究了在酸性pH下非洲（Tibesti）和亚洲（北京）粉尘样品中铁（Fe）的溶解动力学，目的是在大气气溶胶中重现低pH条件。将北京粉尘和Tibesti粉尘的三个尺寸分数（<20μm：PM20; <10μm：PM 10;和<2.5μm：PM2.5）在pH 1、2和/或3下溶解长达1000小时。在最初的10分钟内，所有粉尘样品都经历了极快的铁溶解。随后，Fe的溶解速度要慢得多，直到达到稳定的溶解平台。 Fe随时间变化的数据集最好用一个模型描述，该模型包括三个可酸萃取的Fe池，每个池根据一级动力学溶解。每个池的溶出速率常数k（h〜（-1））与粉尘的来源（撒哈拉沙漠或亚洲）和粉尘大小（PM20，PM10或PM_（2.5））无关，但高度依赖于pH。 “快速”铁池的ak（pH为25 h-1，结合双低线1）的大小与“干燥”亚铁酸盐纳米粒子和/或结晶度较弱的氢氧化三价铁（III）相似，而“中间”和“慢” Fe池的k值分别比“快速”池小50-60倍和3000-4000倍。 “缓慢的” Fe池可能由结晶的Fe氧化物相（即针铁矿和/或赤铁矿）和粘土矿物中所含的Fe组成。 “快”，“中”和“慢”铁池的初始质量分别约占粉尘样品中总铁的0.5-2％，1-3％和15-40％。在粉尘/液体比率低的系统中，铁可以从所有三个池中溶解，而在粉尘/液体比率高的情况下（例如，在气溶胶中），可以从“快”相中溶解出足够的铁以支配溶解的铁，这些数据表明粉尘/液体比和pH是控制粉尘中Fe溶解动力学的基本参数，为了减少大气和气候模型中的误差，这些基本控制因素需要被包括在内。

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