MODELING OF DISPERSION AND ASSESSMENT OF ECOLOGICAL CONSEQUENCES OF CHEMICAL POLLUTION DEPOSITION DURING TECHNOGENIC ACCIDENTS

Abstract

The purpose of the study is to develop a comprehensive mathematical model to forecast and assess not only human impact zones but also the long-term ecological consequences of accidental HDS (Highly Dangerous Substances) releases. The model bridges the gap between classic civil defense tasks and the needs of environmental safety assessment, shifting the focus from calculating toxodose (PC50) to quantifying the mass loading of pollutants onto ecosystems (in kg/ha). The methodology is based on combining two blocks. The first is an improved Gaussian atmospheric dispersion model which, unlike standard approaches, accounts for the surface roughness parameter (z0), significantly impacting near-ground concentrations. The second, and key, block is a newly introduced methodology for calculating dry deposition, which uses the deposition velocity parameter (Vd). This allows for a transition from calculating air concentrations (C) to deposition flux (F) and cumulative deposition (D) onto soil and water. Modeling was performed for scenarios involving a 100-tonne ammonia release under various stability classes (A,D,F) and surface types. The results demonstrate the critical importance of both parameters. First, sensitivity analysis proved that ignoring z0 leads to significant errors in forecasting the cloud dispersion depth (up to an 88% difference under neutral conditions). Second, and most importantly, a quantitative assessment of the ecological impact was conducted. It was demonstrated that the cumulative deposition of ammonia (D) can reach 100…150 kg/ha, which is equivalent to 2…3 years of agricultural nitrogen application norms. This "shock loading" causes acute soil acidification. In water bodies, the calculated concentration (Cwater) reaches 2.5…4.0 mg/L, which critically exceeds the MAC (Maximum Allowable Concentration) for fishery water bodies (<0.5 mg/L) and leads to mass mortality of biota. Limitations and assumptions of the study include the use of parameterized Vd values and the application of a Gaussian model, which is an analytical approximation compared to CFD approaches. The practical value of the work lies in creating a scientific and methodological tool that allows forecasting not evacuation zones, but zones that will require long-term ecological remediation (e.g., soil liming) and enhanced monitoring. The scientific novelty and significance lie in the development of an integrated “atmospheric transport (z0) – deposition (Vd) – ecological consequence (kg/ha, mg/L)” model, which provides a quantitative, rather than merely qualitative, assessment of environmental damage from chemical accidents.