New Model Assesses Urban Spread, CWAs Risks

Abstract

Chemical warfare agents (CWAs) are highly toxic and environmentally persistent, posing human health risks. For example, Venomous Agent X (VX) exhibits low volatility and water solubility, allowing persistence as liquid-phase droplets. To quantify liquid-phase CWA behavior, DREAM-CWA (Dynamic fugacity-based Regional Environmental model for Air-surface exchange and Multimedia fate of Chemical Warfare Agents) was developed as a GIS-based Level IV fugacity model incorporating a droplet compartment. The model estimates phase partitioning and intermedia transport of droplets. Soil, asphalt, coated concrete (non-porous), and water are represented as distinct surface compartments to reflect urban environmental characteristics. Validation against the fugacity model CoZMo-POP 2 confirmed the reliability of DREAM-CWA. A case study of a hypothetical VX chemical attack was conducted as a preliminary evaluation to optimize the multimedia framework, focusing on liquid-phase persistence and multimedia interactions. Initially, VX was retained in droplets and surfaces, with volatilization driving increases in air concentrations. Soil and sediment acted as a dominant short-term reservoir and long-term sink, respectively. Secondary emissions from droplets and surfaces sustained atmospheric exposure. By providing volatilization fluxes resolved in time and space, DREAM-CWA outputs can be coupled with computational fluid dynamics simulations to estimate near-surface dispersion and exposure. This integrated framework offers a robust tool for assessing the environmental risks of CWAs and supporting decision-making during chemical attack responses.

A research team, affiliated with UNIST has reported a new simulation tool to better understand how liquid-phase chemical warfare agents (CWAs) disperse and persist in urban environments. Their findings demonstrate that certain highly toxic chemical agents can remain dangerous even after initial deployment, mainly because droplets that settle on surfaces can evaporate over time and cause secondary exposure.

Professor Sung-Deuk Choi and his team at in the Department of Civil, Urban, Earth, and Environmental Engineering at UNIST, in collaboration with the Agency for Defense Development (ADD) announced the successful development of DREAM-CWA (Dynamic fugacity-based Regional Environmental model for Air-surface exchange and Multimedia fate of Chemical Warfare Agents)-a model designed to predict how liquid chemical agents move and linger after release.

What sets DREAM-CWA apart from existing models is its ability to explicitly consider that chemical agents can stay in droplet form on surfaces, like soil, asphalt, or concrete. The model also divides urban surfaces into categories, allowing for more precise simulations of evaporation rates and how much toxin re-enters the air.

Using DREAM-CWA, the team simulated a scenario where a persistent, highly toxic chemical agent is released in a liquid state at room temperature. The results showed that, 30 minutes after the release, the evaporation of droplets on the ground caused airborne toxin levels to spike 32 times higher than initially, with the amount of toxin released back into the air increasing by about 50%.

This data can be fed into three-dimensional computational fluid dynamics (CFD) models to predict local concentrations of toxic gases at human breathing height-about two meters above ground. By calculating how much toxin is emitted from surface droplets, the CFD simulations can track how the gases spread through complex urban airflow patterns, such as those between buildings.

Professor Choi explained, "Developing a multi-media environmental model that traces the entire process-from chemical release, to droplets, soil, and urban waterways-is a first of its kind, both in Korea and internationally."

Researchers from ADD see this model as a significant step forward. They believe it will enhance existing systems, like NBC_RAMS, enabling more accurate predictions of how liquid chemical agents spread, how people might be exposed, and how long they remain in the environment-crucial information for military responses to chemical threats or terrorist incidents.

The findings of this research have been published in the Journal of Hazardous Materials on December 5, 2025. Supported by the ADD grant, this study was carried out as a commissioned research effort, with Professor Jaejin Kim from Pukyong National University, leading the CFD work.

Journal Reference

Ho-Young Lee, Jeong-Tae Ju, Jae-Jin Kim, "Development and application of a multimedia environmental model for assessing the behavior of chemical warfare agents," J. Hazard. Mater., (2025).