The increase of the industrial production and the development of new processes led to the necessity of better regulations of activities concerning potential risks for human health and environment. Accomplishing such purposes requires studies on both the chemistry of the involved phenomenon and the dispersion mechanism in the surrounding environment. While the chemistry of reaction can be determined at small scale via laboratory experiments and models, the dispersion in the environment is an extremely complex phenomenon to model, because it is strongly affected by the atmospheric conditions. Several models with the purpose of simulating pollutants dispersion were developed (Gariazzo et al., 2012; Alemayehu et al., 2015; Fang et al., 2018); among those, Gaussian models found many applications in safety engineering, due to both their effectiveness and relatively low computational costs. The US-EPA recommends the use of the Gaussian model AERMOD for the simulation of dispersions within 50 km from the emission source. It is important to underline that most of these models were developed with the aim to simulate the dispersion of continuous emissions such as those from industrial chimneys. Such systems can be assumed to work under steady-state conditions, since they are supposed to work for a long time. Nonetheless, industrial accidents, which can have a severe impact on people and environment, generally occur at a relatively small time scale, thus their dispersion has not yet reached the steady state conditions.
In this work, we developed a modified non-steady-state Eulerian Gaussian model able to simulate the dispersion of contaminants produced by an industrial accident, which is hypothesized to be a point source. The model requires as input data time-dependent meteorological conditions and topographic information of the site, concerning: the source, physical properties of the pollutant, emission height and release temperature. The proposed model was applied to the 2,3,7,8-Tetrachlorodibenzodioxin (TCCD) dispersion after the Seveso accident (1976) near the source (radius of about 4 km). Results highlighted a good agreement with available literature experimental data.