Source Parameter Estimation of Atmospheric Pollution from Accidental Gas Releases

Abstract

This paper presents the development of an inverse model that may be used to estimate the source term parameters for a polluting gas released into the atmosphere from a point above the ground. The model uses measured pollution concentrations at observation sites on the ground as well as meteorological data such as wind speed and cloud cover. The inverse model is formulated as a least- squares minimisation problem coupled with the solution of an advection-dispersion equation. The minimisation problem where the pollutants are released instantaneously is well-posed and the source term is calculated with reasonable accuracy. However, the problem with a non-steady extended release source is ill-posed; consequently, its solution is extremely sensitive to errors in the measurement data. Tikhonov's regularisation, which stabilises the solution process, is used to overcome the ill-posedness of this problem and the regularisation parameter is estimated using the properties of the non-linear L-curve, and Wahhba's leaving-out-one lemma. Finally, the accuracy of the model is examined by imposing normally-distributed relative noise into concentration data generated by the forward model.