PAHs distribution variations

Equilibrium partitioning was observed with trichlorobiphenyls and the chlorobenzenes, while the tetra- and pentachloro dioxins and furans, and heptachloro-biphenyls distributed into the vegetation by kinetically limited gaseous uptake. Octochloro dioxins and furans along with the higher molecular weight PAHs distributed onto plants by particle deposition. This would be consistent with the known propensity of the latter to distribute onto particles. These data also provide an opportunity to evaluate differences among plant species and the ratio of surface to volume accounted for much of the variation observed. 

The absorption of ozone from the gas occurred simultaneously with the reaction of the PAH inside the oil droplets. In order to prove that the mass transfer rates of ozone were not limiting in this case, the mass transfer gas/water was optimized and the influence of the mass transfer water/oil was studied by ozonating various oil/water-emulsions with defined oil droplet size distributions. No influence of the mean droplet diameter (1.2 15 pm) on the reaction rate of PAH was observed, consequently the chemical reaction was not controlled by mass transfer at the water/oil interface or diffusion inside the oil droplets. Therefore, a microkinetic description was possible by a first order reaction with regard to the PAH concentration (Kornmuller et al., 1997 a). The effects of pH variation and addition of scavengers indicated a selective direct reaction mechanism of PAH inside the oil droplets... 

Several compounds were also found to have a seasonal distribution. Kubatova et al. (2002) found that concentrations of lignin and cellulose pyrolysis products from wood burning were higher in aerosol samples collected during low-temperature conditions. On the other hand, concentrations of dicarboxylic acids and related products that are believed to be the oxidation products of hydrocarbons and fatty acids were highest in summer aerosols. PAHs, which are susceptible to atmospheric oxidation, were also more prevalent in winter than in summer. These results suggest that atmospheric oxidation of VOCs into secondary OAs and related oxidative degradation products are key factors in any OA mass closure, source identification, and source apportionment study. However, additional work is much desirable to assess the extent and seasonal variation of these processes. 

The size distribution of air particles not only influences the distribution and partitioning dynamics of POPs, but also determines dry and wet deposition flux of POPs. An interesting phenomenon was observed for relationship among atmospheric PAHs, particle size distribution, and the levels of PAHs in soil (Kim, 2004). For urban sites, the composition pattern and absolute concentrations of PAHs in soil were well correlated with those in air where the atmospheric particles size was distributed evenly among seasons with predominant amount of fine particles < 3 pm. Dry deposition flux of PAHs followed seasonal variation in atmospheric concentration in urban site. However, at a suburban site with large seasonal variation in particle size distribution, dry deposition flux and soil residue did not reflect the seasonal variation of atmospheric PAHs. From this result, site-specificity in atmospheric particle distribution may also influence the distribution and residues in the underlying soil. 

In the same city, the distribution patterns of PAHs were examined in four interactive main aspects PAHs composition, spatial distribution, seasonal variation, gas phase and particle size distribution and vertical distribution. 

Producing PAH isolates by a general scheme from complex, fossil-derived materials is made difficult by the wide variation in sample characteristics. The scheme presented here requires considerably more study to determine general applicability and actual separation efficiencies, but preliminary data indicate much promise in this approach. Figure 2 shows the sequence of steps which involve three-solvent distributions and two-column chromatographic purifications. A typical separation proceeds as follows (1) 1-2 g of crude liquid are dissolved in 500 mL... 

Letelier RM, Dore JE, Winn CD, Karl DM (1996) Seasonal and interannual variations in photosynthetic carbon assimilation at station ALOHA. Deep Sea Res Part II Top Stud Oceanogr 43(2-3) 467-490 Li B, Wu Y, Zhang J (2002) Distribution and source of polycychng aromatic hydrocarbons (PAHs) in surface sediment of the northern Yellow Sea. Chin Environ Sci 22(5) 429-432 (in Chinese with English abstract)... 

Bae SY, Yi SM, Kim YP (2002) Temporal and spatial variations of the particle size distribution of PAHs and their dry deposition fluxes in Korea. Atmos Environ 36 5491-5500 Behymer TD, Hites RA (1988) Photolysis of polycyclic aromatic hydrocarbons adsorbed on fly ash. Environ Sci Technol 22 1311-1319... 

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