Emission-limited discharge model

Known models describing emission-limited discharge differ in mechanisms responsible for the charge transfer from the surface into the bulk. Most often these mechanisms include Schottky emission, tunneling, and thermal activation fiom discrete traps (Abkowitz et al. 1995 Kressman et al. 1999 Sessler 1999). Publications that allow for the continuous spectrum of surface traps are relatively few in number (Watson 1990 Watson et al. 1991), although the need for such an approach is obvious due to the highly disordered nature of the polymer surface. 

All detection limits are given in micrograms per liter and were determined using elemental standards in dilute aqueous solution. All detection limits are based on a 98% confidence level (3 S.D.). All atomic absorption (Model 5100) detection limits were determined using instrumental parameters optimized for the individual element, including the use of system 2 electrodeless discharge lamps where available. ICP emission (Optima 3000) detection limits were obtained under simultaneous multielement conditions with a radial plasma. Detection limits using an axial plasma (Optima 3000 XL) are typically improved by 5-10 times. 

The Gaussian dispersion model has several strengths. The methodology is well defined and well validated. It is suitable for manual calculation, is readily computerized on a personal computer, or is available as standard software packages. Its main weaknesses are that it does not accurately simulate dense gas discharges, validation is limited from 0.1 to 10 km, and puff models are less well estabUshed than plume models. The predictions relate to 10 min averages (equivalent to 10 min sampling times). While this may be adequate for most emissions of chronic toxicity, it can underestimate distances to the lower flammable limit where instantaneous concentrations are of interest. More discussion will follow. 

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