Applicable conditions of point source diffusion model and smoking model

1. The smoke flow diffused by fumigation was originally in a stable stratified state, and then pollutants accumulated to the ground through fumigation. The smoke diffusion process lasts for a short time.

2. The closed diffusion smoke flow was originally in unstable stratification, and pollutants did not accumulate, which had a light impact on the ground. The closed diffusion process often lasts for a long time.