HarmoNIES No.4

How can we know what chemicals are moving around in the environment? Chemicals are very small and, of course, not directly visible to the human eye. If they are dissolved in water or dispersed in the atmosphere, it is impossible to follow them visibly (Picture1). How then can we track them? To meet this challenge, Dr. Imaizumi uses computer models. With models like these, we can create a simulated environment on a computer and calculate the movement of chemical substances in that environment. In other words, he builds a "model environment" on the computer.


There are many different types of environments, including the atmosphere, oceans and rivers, soil, sand, and clay. Considering each as a “box”, we can calculate the movement of chemicals in and out of the box (Picture2). This is the basic concept underlying a model used for the entire environment (the model is called G-CIEMS). As the box becomes more detailed, we can expand the spatial extent of our calculations. By doing so, we can follow the movement of chemicals over a larger area and areas that have not even been surveyed. In this process, we can, for example, simulate how the seasonal concentration of pesticides used in rice fields changes in rivers or understand the movement of radioactive materials from nuclear accidents. That’s wonderful! However, each chemical varies in the ways they spread in the environment, it is important to design the “boxes” according to the natures of the chemical substances we want to learn about. It is also very important to select the environment to focus on, whether it is the entire environment, or a particular part of it, such as the atmosphere or a coastal area. Sometimes, to gain a more comprehensive understanding, we need to combine several of these factors in the model calculations.