Monitoring of fogwater chemistry in the gulf coast urban industrial corridor: Baton Rouge (louisiana).

Seventeen fog events were sampled in Baton Rouge, Louisiana during 2002-2004 as part of characterizing wet deposition by fogwater in the heavily industrialized corridor along the Louisiana Gulf Coast in the United States. These samples were analyzed for chemical characteristics such as pH, conductivity, total organic and inorganic carbon, total metals and the principal ion concentrations. The dominant ionic species in all samples were NH4+, NO3-, Cl- and SO4(2-). The pH of the fogwater sampled had a mean value of 6.7 with two cases of acidic pH of 4.7. Rainwater and fogwater pH were similar in this region. The acidity of fogwater was a result of NO3- but partly offset by high NH4+. The measured gaseous SO2 accounted for a small percentage of the observed sulfate concentration, indicating additional gas-to-particle conversion of SO2 to sulfate in fogwater. The gaseous NOx accounted for most of the dissolved nitrate and nitrite concentration in fogwater. The high chloride concentration was attributable to the degradation of chlorinated organics in the atmosphere. The metal composition was traced directly to soil-derived aerosol precursors in the air. The major metals observed in fogwater were Na, K, Ca, Fe, Al, Mg and Zn. Of these Na, K, Ca and Mg were predominant with mean concentrations > 100 microM. Al, Fe and Zn were present in the samples, at mean concentrations < 100 microM. Small concentrations of Mn (7.8 microM), Cu (2 microM), Pb (0.07 microM) and As (0.32 microM) were also observed in the fogwaters, and these were shown to result from particulates (PM2.5) in the atmosphere. The contribution to both ions and metals from the marine sources in the Louisiana Gulf Coast was minimal. The concentrations of all principal ionic species and metals in fogwater were 1-2 orders of magnitude larger than in rainwater. Several linear alkane organic compounds were observed in the fogwater, representing the contributions from petroleum products at concentrations far exceeding their aqueous solubility. A pesticide (atrazine) was also observed in fogwater, representing the contribution from the agricultural activities nearby.

Soil-water partitioning and desorption hysteresis of volatile organic compounds from a Louisiana Superfund site soil.

The adsorption and desorption of three volatile organic compounds (1,2-dichloroethane, 1,1,2- trichloroethane and 1,1,2,2-tetrachloroethane) from a previously uncontaminated clayey soil sample from a Superfund site in North Baton Rouge, Louisiana was studied. In the linear range of the adsorption isotherm, the partition constants were not affected by the presence of the co-solutes. The adsorption isotherms over a wide concentration range on the soil followed the nonlinear Freundlich isotherm. The desorption of the compounds showed significant hysteresis at all concentrations studied. Approximately 20 to 70% of the adsorbed mass of organic compounds resisted the desorption even after five months of successive desorption steps. The desorption of four compounds (1,2-dichloroethane, 1,1,2-trichloroethane, 1,4-dichlorobenzene and hexachlorobutadiene) from a contaminated soil sample from the same site was also studied. The aqueous concentration declined as the successive desorption steps progressed. For hexachlorobutediene the desorption can be visualized as occurring in two stages. The first stage involved a 'loosely bound' or 'reversible' fraction and the second stage involved a 'tightly bound' or 'resistant' fraction.

Rate-limited desorption of volatile organic compounds from soils and implications for the remediation of a Louisiana Superfund site.

The rates of desorption of trichloroethylene (TCE) and 1,3-dichlorobenzene (DCB) from a silty soil at a Superfund site and a silty-clayey soil from an uncontaminated bottomland hardwood swamp in Baton Rouge, Louisiana were studied in laboratory batch systems. The effect of the age of soil contamination was studied using a laboratory-spiked soil incubated for 3 days, 3 months and 5 months. An empirical non-linear model was used to describe the bi-phasic nature of desorption with one fraction (labile) being released in relatively short periods of time (typically 24-100 hr) and a second fraction (non-labile or irreversible) being resistant to desorption. The non-linear model parameters, viz., the fraction of the chemical released rapidly (F), and the first order desorption rate coefficients, k1 and k2 respectively for the labile and slowly released fractions were determined by fitting the experimental data to the model. The data fit the model well as indicated by the high r2 values. The estimate of k1 was good. However, the values of k2 are known with less precision due to the limited duration of the experiment and number of samples taken at long times. In addition, desorption kinetics of 3 and 5-month old contaminated soils showed that progressively less amount of contaminant was available for facile desorption (lower F) compared to freshly contaminated soil. The labile fraction had desorption rate constants of the order of 10(-1) h(-1), whereas the slowly released fraction had rate constants of the order of 10(-4) h(-1) in accord with literature reported values for a variety of other compounds and soils. Possible mechanisms describing these rates and implications for the site clean up are discussed.