What measures can be taken to reduce the health effects of hazy days? There are four main measures: First, masks. Personally, I think we need to wear a mask when the PM2.5 index is greater than 100. Second, the air purification of the environment. That is, when the PM2.5 index is large, the location of work and study with air purification devices to purify. Third, escape. When the pollution is serious, reduce outdoor activities. Go to a location with good air when resting. Special emphasis, do not exercise outdoors when pollution is heavy. Fourth, aerobic exercise. Enhance human function and improve immunity. What kind of mask to choose? Regarding the choice of masks, first of all, choose a reputable brand, such as 3M’s. Because we cannot identify the purification effect of the mask, the reputation of the business is very important at this point. Furthermore, when we wear the mask, we must seal it tightly all around, because the air will go to the position of less resistance, and if it is not sealed tightly, most of the air will flow in from there, making the purification effect discounted. From this reasoning, we know that the kind of mask that only inserts a consideration piece in the front is not very meaningful. Even if it has a good effect, most of the air flows in from all around the edge. Furthermore, the mask should be used according to the instructions and should be replaced frequently. Are air purifiers useful? Air purifiers are useful. At least partially. And also choose a reputable brand. In addition, be careful to close the window when using it. When you leave, be careful to open the window to change the air. Do I need to open the windows to ventilate on a hazy day? Yes, we do. Because we need fresh oxygen and air flow. It is better to open the windows when we are not at home.