Atmospheric trace metals over the south-west Indian Ocean: Total gaseous mercury, aerosol trace metal concentrations and lead isotope ratios
Atmospheric trace metals over the south-west Indian Ocean: Total gaseous mercury, aerosol trace metal concentrations and lead isotope ratios
复制标题
DOI：
10.1016/j.marchem.2010.02.005
复制
发表时间：
2010-08
期刊：
影响因子：
3
通讯作者：
M. Witt;T. Mather;A. Baker;J. D. Hoog;D. Pyle
中科院分区：
文献类型：
--
作者：
M. Witt;T. Mather;A. Baker;J. D. Hoog;D. Pyle
对从塞舌尔到毛里求斯的印度洋航行期间收集的气溶胶和雨水样本中的痕量金属（Al、Fe、Ba、Mn、Co、V、Cr、Mo、Sr、Pb、Cd、As、Zn、Cu和Ni）和主要离子（Na+、Mg2+、Ca2+、K+、NH4+、Cl −、NO3 −、SO42 −和草酸盐）的大气浓度进行了分析。在航行期间还进行了半连续的气态汞总量测量。南半球海洋大气中痕量金属的数据很少，特别是汞，这是首次报告印度洋这一部分的TGM浓度。巡航期间总汞浓度为1.05 - 1.51 ngm − 3（平均1.2 ngHgm − 3），接近北方半球海洋观测到的汞浓度的下限。TGM数据似乎显示了巡航期间的浓度梯度，在更靠近热带辐合带的北方位置浓度增加。在气溶胶中的一些微量金属中也观察到这种趋势。气团的反向轨迹表明，在收集之前，遇到的空气至少在海洋上空停留了五天。富集因子的计算表明，As，Pb，Ni，Cu，Cd，Zn和Cr在一定程度上富集以上的地壳和海洋来源的气溶胶中的金属。测量气溶胶样品中的总金属浓度以及可溶于pH 4.7缓冲液和pH 1硝酸的部分。对于Fe，这些分数分别为<5%和> 13%。铝和铁的溶解度显着高于pH 1的硝酸比pH 4.7的缓冲液，但对于其他金属的研究没有显着差异。大部分的镉，锌和砷的气溶胶中很容易溶解在pH 1的硝酸和pH 4.7的缓冲液。镍、铜和铅在这些溶液中的溶解度更有限（在pH 4.7缓冲液中分别为63、72和69%;在pH 1硝酸中分别为60、72和57%）。还测量了气溶胶样品中稳定的铅同位素比率，以调查其来源。对于大多数气溶胶样品，Pb同位素聚集在相当小的放射成因值范围内（207Pb/206Pb 0.84 - 0.85，208Pb/206Pb 2.03 - 2.07）。铅同位素与气溶胶粒度级没有显着的趋势。同位素比值是一致的增加的重要性，煤炭燃烧作为铅的来源在印度洋。
Atmospheric concentrations of trace metals (Al, Fe, Ba, Mn, Co, V, Cr, Mo, Sr, Pb, Cd, As, Zn, Cu and Ni) and major ions (Na+, Mg2+, Ca2+, K+, NH4+, Cl−, NO3−, SO42−and oxalate) were analysed in aerosol and rain samples collected during an Indian Ocean cruise from Seychelles to Mauritius. Semi-continuous total gaseous mercury (TGM) measurements were also made during the cruise. Data for trace metals in the marine atmosphere is sparse for the southern hemisphere, particularly for Hg, and these are the first reported TGM concentrations for this part of the Indian Ocean. TGM was 1.05–1.51ngm−3during the cruise (average 1.2ngHgm−3), towards the lower end of mercury levels observed over oceans in the northern hemisphere. The TGM data appears to show a concentration gradient over the cruise with increasing concentrations at more northern locations closer to the inter-tropical convergence zone. This trend was also observed in some of the trace metals in aerosols. Air mass back trajectories suggest the air encountered had spent at least five days over the ocean prior to collection. Enrichment factors were calculated for the metals in the aerosols which suggested As, Pb, Ni, Cu, Cd, Zn and to some extent Cr were enriched above both crustal and oceanic sources. The total metal concentrations were measured in the aerosol samples along with the fraction soluble in pH 4.7 buffer and pH 1 nitric acid. For Fe these fractions were <5% and ∼13% respectively. The solubility of Al and Fe was significantly higher in pH 1 nitric acid than pH 4.7 buffer, but for the other metals studied there was no significant difference. Most of the Cd, Zn and As in the aerosols was readily soluble in both pH 1 nitric and pH 4.7 buffer. Nickel, Cu and Pb solubility in these solutions was more limited (in pH 4.7 buffer 63, 72 and 69%; in pH 1 nitric acid 60, 72 and 57% respectively). Stable lead isotope ratios were also measured in the aerosol samples to investigate their origin. For most of the aerosol samples, the Pb isotopes clustered within a small range of fairly radiogenic values (207Pb/206Pb 0.84–0.85,208Pb/206Pb 2.03–2.07). No significant trend was found for Pb isotopes with aerosol size fractions. The isotope ratios are consistent with an increased importance of coal combustion as a source of Pb over the Indian Ocean.