PubMed · 10244352
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E A Cox. 1979-11-12. The night we worked through hell.. https://pubmed.ncbi.nlm.nih.gov/10244352/
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Microwave plasmas at 2.45 GHz frequency operated at atmospheric pressure in synthetic gas mixtures containing N2 and CF4 are investigated experimentally for various operating conditions, with respect to their ability to destroy perfluorocompounds. It was found that the destruction and removal efficiency of the process is highly dependent on the total gas flow and concentration of CF4. Destruction and removal efficiencies of CF4 up to 98% have been achieved using 1.9 kW of microwave power at 16 L/min total flow rate.
A probabilistic model called the potential source contribution function (PSCF) has been used to estimate atmospheric source regions of polycyclic aromatic hydrocarbons (PAHs), chlorinated pesticides, and polychlorinated biphenyls (PCBs) to the Great Lakes. This model allows us to map each compound's source region on a 0.5 degrees x 0.5 degrees latitude/longitude grid centered over the Great Lakes basin. PCBs primarily have urban sources, the strengths of which vary. Like PCBs, PAHs show a strong urban signature, but these compounds also seem to come from rural sites. The source regions of PAH become less distinct as the molecular weight of the compound increases. Since reactivity increases with PAH size, this diminishing trend may be an indication that atmospheric degradation plays a large role in PAH transport. The pesticides have the strongest source regions and are typically transported the farthest, often from areas distant from the Great Lakes basin.
A coupled atmospheric transport, soil-air, water-air exchange model was developed to investigate the impacts of gamma-hexachlorocyclohexane (gamma-HCH or lindane) usage in the Canadian prairies over the Great Lakes region. The fate of gamma-HCH in air and soil is governed by atmospheric dynamics and physical and chemical processes that are described by the coupled model. These processes include transport and turbulent diffusion in the atmosphere, dry and wet deposition, exchange at the interfacial boundaries of air-water and soil-air, and removal processes from the soil such as diffusion, leaching, and degradation. Numerical experiments were conducted for the period of May 1, 1998-April 30, 1999, starting with application of lindane in the spring. The coupled model was executed with two lindane emission (usage) inventories in the model domain. The first scenario contained all known fresh emission sources in Canada-98% was usage in the prairies; the second excluded emission sources from Ontario and Quebec. The model showed that, in the absence of the reemission from past application of lindane, usage of lindane in Ontario and Quebec has a negligible impact on air concentrations in these regions and that the lindane budget in the Great Lakes ecosystem is mostly attributed to applications of lindane in the canola fields in Canadian prairie provinces. Model-predicted air concentrations and seasonal trends agreed well with measured data over the same time period for several background sites operated under the Integrated Atmospheric Deposition Network. Air temperature was shown to play a key role on surface-air exchange dynamics of gamma-HCH. A future paper will assess loadings to the Great Lakes based on these validated model results.