Biogenic background

Simoneit, B.R.T., and Mazurek, M.A. (1982) Organic matter of the troposphere—II. Natural background of biogenic lipid matter in aerosols over the rural western United States. Atmos. Environ. 16, 2139-2159. 

The sedimentation is strongly controlled by the inherited character of the relief-forming processes that proceeded against the background of the Holocene history of the Black Sea. Sediment formation is also influenced by the solid riverine runoff and coastal abrasion, slope-derived supply, and biogenic and chemogenic matter. 

Oxidation of hydrocarbons has long been considered as a fundamental problem to atmospheric chemists, both from experimental and theoretical points of view, because of the inherent complexity. The reaction kinetics and mechanism of atmospheric hydrocarbons have been the focuses of numerous researches in both experimental and theoretical aspects. Although advances have been made in elucidation of the VOC oxidation mechanisms, large uncertainty and tremendous numbers of unexplored reactions still remain. Several review articles on the atmospheric degeneration of VOCs have been published [4,11-14]. In this review, recent advances in the application of theoretical methods to the atmospheric oxidation of biogenic hydrocarbons are discussed. We will introduce the backgrounds on the quantum chemical calculations and kinetic rate theories, recent progress on theoretical studies of isoprene and a-, y3-pinenes, and studies on other monoter-penes and sesquiterpenes. 

The proportion of female Sprague-Dawley rats developing mammary tumors decreases very rapidly as the dose decreases (American Biogenics Corporation, 1986 McCormick, 1988 Thakur, 1991, 1992). The observed dose-response relationship is sublinear. Furthermore, the biological mechanism by which atrazine and simazine cause this response is most likely a threshold mechanism thus, the sublinear dose-response relationship contains a range of positive doses for which the frequency of the response is not increased above the background frequency at zero dose (Andersen et al., 1998 Connor et al., 1998 Eldridge et al 1998 Simpkins et al, 1998). 

Sediment and oyster samples collected approximately 25 km downstream at the mouth of the river, produced chromatograms indicating primarily biogenic hydrocarbons (Site b-6. Figure 5), providing excellent background data for comparison in the event of a future oil spill. 

In addition to this published data we identified several non-halogenated contaminants, which are also specific for this local emission due to their obviously non-biogenic structures and the point source related spatial distribution. In detail, 4-nitrobenzoic acid [ 1] was only detected at sampling locations T1 and T2 situated nearby the industrial point source (see Table 4). Also in samples T1 and T2 the concentrations of 4-ethylnitrobenzene [ 2], formylpiperidine [ 3] and acetylpiperidine [ 4] increased significantly up to 61, 39 and 28 ng/g, respectively (see Table 3), compared to stations T5 and T6, which are assumed to be contaminated only by diffuse sources, representing therefore background samples with respect to the industrial point source. 

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