Particles in the air will move vertically up and down with the airflow. Generally speaking, particles in the air will rise with the airflow. This vertical movement is also accompanied by horizontal diffusion, and pollutants in the city slowly spread.
In many cities, the phenomenon of "inversion" often occurs in winter. On the contrary, the temperature in the upper air is higher than that near the ground, and the airflow cannot rise when it reaches the top of the inversion layer, which compresses the area where air can circulate, making it difficult for pollutants to spread near the ground. Even under special meteorological conditions such as inversion, the air circulation layer over the city is often as high as hundreds of meters to thousands of meters. Ordinary buildings shall not exceed 100 meter. Even if there is an inversion, the air on all floors is polluted by smog. It is unfounded to say that the higher the floor, the lower the concentration of PM2.5.
It is suggested that if the outdoor air pollution is not serious, citizens can improve the indoor air quality by opening the window for a short time at ordinary times, and they don't have to dare to open the window for ventilation because they are worried that outdoor pollution will enter the room with the wind.