Frequency distributions of anthracene and pyrene in the topsoil of Tianjin
天津地区表土中蒽和芘的频率分布特征

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 three-division-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\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.