本研究通过集成包括多环芳烃的组成、特征比值、铅稳定同位素和正定矩阵因子模型等多种源解析方法，并在中国南海北部加以应用，首次定量出不同热解来源的历史变化，并逐步反演出能源结构的历史变化趋势。在空间分布上，铅和多环芳烃浓度呈现离岸逐渐降低的趋势，但是最高的浓度却出现在台湾海海峡南部，这可能是不同河流输入汇聚的结果。它们的历史变化与中国的经济发展密切相关，含铅汽油的逐步淘汰使得铅浓度在20世纪九十年代后呈现快速降低的趋势。源解析结果表明，生物质燃烧、煤燃烧和汽车尾气排放分别贡献了40 ± 20%, 41 ± 13%, 和19 ± 12%的多环芳烃。2000年以前，煤和生物质燃烧是主要贡献者，但是汽车尾气的排放在2000以后高涨。本研究从逐步推进和交叉验证的角度提高了源解析的可信度，并可以应用到其他水环境中。
Fig.1 Spatial distributions of PAHs (a) and Pb (b) concentrations in the NSCS.
Fig.2 Temporal trends of (a) Pb contents; (b) variations of ∑15PAHs and PAHs with different rings; (c) average relative abundance of PAHs with different rings.
Fig. 3 Plots of 206Pb/207Pb versus 208Pb/207Pb isotopic ratios of pollution core-samples in comparison with various pollution sources and natural backgrounds (Zhu et al., 2001; Bollhofer and Rosman 2001; Lee et al., 2007; Chen et al., 2005; Mukai et al., 2001; Zhu et al., 2010; Hsu et al., 2006; Mukai et al., 1993; Mukai et al., 1994; Ip et al., 2007). The green star and the pentagon represent aerosols from Japan and Taipei.
Fig. 4. (a) Compositional profiles of the PAH compounds in three factors obtained from the PMF model and from typical combustion emissions (data were summarized and reanalyzed from previous studies) (Tables 10-12). (b) Temporal changes in the PAH contributions of different sources (biomass burning, coal combustion and vehicle emissions) of PAHs obtained from the PMF model.
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ABSTRACT
To obtain the historical changes of pyrogenic sources, integrated source apportionment methods, which include PAH compositions, diagnostic ratios (DRs), Pb isotopic ratios, and positive matrix factorization (PMF) model, were developed and applied in sediments of the northern South China Sea. These methods provided a gradually clear picture of energy structural change. Spatially, Σ15PAH (11.3 to 95.5 ng/g) and Pb (10.2 to 74.6 μg/g) generally exhibited decreasing concentration gradient offshore; while the highest levels of PAHs and Pb were observed near the southern Taiwan Strait, which may be induced by accumulation of different fluvial input. Historical records of pollutants followed closely with the economic development of China, with fast growth of Σ15PAH and Pb occurring since the 1980s and 1990s, respectively. The phasing-out of leaded gasoline in China was captured with a sharp decrease of Pb after the mid-1990s. PAHs and Pb correlated well with TOC and clay content for core sediments, which was not observed for surface sediments. There was an up-core increase of high molecular PAH proportions. Coal and biomass burning were then qualitatively identified as the major sources of PAHs with DRs. Furthermore, shift toward less radiogenic signatures of Pb isotopic ratios after 1900 revealed the start and growing importance of industrial sources. Finally, a greater separation and quantification of various input was achieved by a three-factor PMF model, which made it clear that biomass burning, coal combustion, and vehicle emissions accounted for 40 ± 20%, 41 ± 13%, and 19 ± 12% of PAHs through the core. Biomass and coal combustion acted as major sources before 2000, while contributions from vehicle emission soared thereafter. The integrated multi-methodologies here improved the source apportionment by reducing biases with a step-down and cross-validation perspective, which could be similarly applied to other aquatic systems. |
