Keywords: ADMS, clipped-normal distribution, correlations, exceedences, fluctuations, turbulence
Turbulent fluctuations and their use in estimating compliance with standards and in model evaluation
Turbulent fluctuations are important in dispersion problems where short timescale peak values can be critical. These situations include: a) releases of toxic, flammable or odourous substances where high short time scale impacts may be dangerous or cause a nuisance; b) estimating concentrations for regulatory purposes for comparison with limits based on a short timescale, such as the UK 15-minute or WHO 10-minute levels for SO2; c) assessing the uncertainties in dispersion model predictions and aiding model comparison with measured data. The ADMS 3 dispersion model includes a module to calculate turbulent fluctuations which is based on a "two particle dispersion" concept but has much in common with Gifford's meandering plume model. It has been used in critical applications where odour and exceedences of a regulatory value were the issues. In this paper, the fluctuations model is described and each of the three applications is illustrated.