Evaluation of atmospheric dilution factors for effluents diffused from an elevated continuous point source

Abstract

Using the wind vector fluctuations measured at a height of 69 m by a tridimensional anemometer, the standard deviations au and a, of the lateral and vertical distributions of the effluents emitted by an elevated continuous point source have been computed. Nearly 300 hourly tests covering most of the weather conditions to be encountered on the Mol site have been made, during which have also been determined the values of a stability parameter S defined as the ratio of the hourly mean of the vertical gradient of the potential temperature between 8 and 114 m to the square of the hourly mean wind speed at 69 m. The dependence functions uu op = f(S) are of the hyperbolic type for S > 0 as well as for S < 0; they apply for hourly mean wind speeds up to 11.5 m s-I. For the sake of simplicity and quick estimations of uu and a, for current practical uses, seven atmospheric stability categories have been defined with the corresponding median uu and a, values at different downwind distances z. When ti < 11.5 m.s-l, categories El to E, are differentiated by means of a parameter f. derived from S by f.= log,, [IS I .lo6]; category E, corresponds to the case of strong winds.The data obtained show that for downwind distances z up to 50 km, the standard deviations au and a, dependon z following a power law. The Yo1 theoreticalresults compare favourably with those found by means of field experiments carried out on the Mol site as well as elsewhere by other authors.

Short-range diffusion experiments in unstable conditions over inhomogeneous terrain

“…The Taylor diffusion formula using the wind velocity measurements at the height of release was found to work well in predicting uy, despite the fact that shortcomings in fulfilling the requirements for its application existed. uy, predicted by an empirical formula characteristic for an open area (Bultynck and Malet, 1972), was found to be systematically larger than the experimental value. Excellent agreement was found by multiplying the predicted 0 , .…”

“…For comparison, the lateral and vertical standard deviations, ay and a, , are derived: according to formulae, (ay),,,, and (u~)~,, given by the ASME's Recommended guide for the prediction of the dispersion of airborne efluents, edited by Smith (1968b), which used a qualitative classification of the atmospheric stability; according to a method given by Bultynck and Malet (1972), and ( a, ) , , using a quantitative description of the atmospheric stability; and by a statistical treatment of the wind fluctuation measurements, (a, ), , , and following an appropriate mathematical model. Smith's (1968b) formulae for a, and a, are considered to be valid for elevated sources and a sampling period of 1 h. Atmospheric stability is classified as stable, neutral, unstable and very unstable, and formulae are given for each class.…”

“…Formulae for uy and a, as a function of the parameter S = (a9/az)/ziz are given in Bultynck and Malet (1972), M / a z is the vertical potential temperature gradient and z i the mean wind velocity at the height of release. The S parameter is a quantity often used to characterize the atmospheric stability conditions (Hanna, 1977).…”

“…Consequently, the formulae are site-specific. The Bultynck and Malet (1972) formulae are for an elevated source, 69 m high, and are derived by application of the Taylor diffusion formula to wind fluctuation measurements at the release height. The formulae apply to the Belgium S.C.K./C.E.N.…”

An On Line Atmospheric Dispersion Model (OLADMO) for the World Wide Web

“…HPDM, OML and UK-ADMS are next generation models, parameterising atmospheric turbulence and stability by the Monin-Obukhov length and boundary layer depth. IFDM utilises the Bultynck-Malet stability classification (Bultynck and Malet 1972) which assesses stability by the potential temperature gradient and wind speed at 69 m. Stability in INPUFF is determined by the Pasquill-Gifford stability class. However, INPUFF differs from other models by being a puff and not a continuous emission model; it therefore calculates concentrations by a different method to that used for standard Gaussian plume models.…”