天津地区表土中蒽和芘的频率分布特征

Frequency distributions of anthracene and pyrene in the topsoil of Tianjin

用频率分析、逐步聚类和最小二乘拟合等方法研究了天津地区表土中蒽和芘含量的频率分布特征。结果表明,两者都呈双峰分布,其中蒽的双峰特征尤为典型。可以用双高斯密度函数很好地拟合经对数变换的实际观测数据,证明天津地区蒽和芘都包括两个相对独立的对数正态分布总体。根据拟合频率密度函数求得的蒽的两个子总体几何均值分别为2.73±2.17ng/g和26.52±1.55ng/g,芘则为11.05±2.11ng/g和82.52±3.24ng/g。芘的两个总体在空间上的分异比蒽更明显,其高值总体主要集中在城区、近郊区和开发区,而蒽的高值总体仅有局部聚集的一般趋势。芘与芘/苯并[a]芘之比的空间分布特征十分相似,表明两个芘含量总体并存的原因与排放源特征有关。

Frequency distributions of contaminants in special medium can reflect from one profile its macroscopic statistic characteristics, and can also supply necessary basic information for the classical, multivariate and spacial statistic analysis, so as to ensure basic needs to all kinds of methods for statistic analytical data. So for special studies on statistic distribution characteristics of PAH content with large numbers of specimen in a vast region have been rarely seen. Characteristics of frequency distributions of anthracene and pyrene in the topsoil of Tianjin, China, which was polluted seriously by PAHs, were studied based on frequency analysis, K-Means clustering and least-square fitting. It was demonstrated that both anthracene and pyrene, especially the former, are bimodally distributed. Double gaussian function can be used to fit the empirical distribution well after log-transformation, suggesting the presence of two independent lognormally distributed populations for either anthracene or pyrene. The geometric means of the two populations were 2. 73±2.17 ng/g and 26.52± 1.55ng/g for anthracene and 11.05± 2.11ng/g and 82.52±3.24ng/g for pyrene. Hereby, the research which adopts two-division-methods and threedivision-methods indicates： that the spatial separation of the two pyrene populations is explicitely illustrated by symbol mapping, showing that the indiviudals of the high value population clustered in urban, near-suburb, and newly developed industrial areas. For anthracene, there is a tendency of local clustering. Besides, the similarity between the spatial distribution patterns of pyrene and pyrene/benzo[a]pyrene ratio suggests that the dual-modal distribution of pyrene was emission-source related. Fitting and separating methods of multi-modal distributions mentioned above provided methodological grounds for deep probing into their differences and origins of the distributive characteristics of different PAHs.