First, we need to understand a concept of diffusion. That is to say, the substance will move from the area with high concentration to the area with low concentration, and finally tend to be in equilibrium, just like water will flow from high to low. Dropping a drop of ink into a glass will soon blacken the whole glass. The same is true of gas, although we can't see it. Before the treatment, there will be formaldehyde in the air and materials, which will reach a balanced state. When using gas catalyst, the main effective component of gas catalyst is gaseous chlorine dioxide, which will react with formaldehyde, and formaldehyde will be converted into carbon dioxide and water by reaction, so the concentration of formaldehyde in the air will be reduced. Once the concentration of formaldehyde in the air is reduced, the formaldehyde in walls, furniture and other materials will accelerate to diffuse into the air to participate in the reaction. In this way, after a long period of closed reaction, formaldehyde is almost removed.