The appearance of heavily polluted weather mainly depends on which two factors.

The emergence of heavily polluted weather mainly depends on: high emission intensity of pollutants and unfavorable meteorological conditions. Heavily polluted weather refers to the phenomenon that the air quality index is greater than 200, that is, the ambient air quality reaches the level of heavy pollution and above; Heavy polluted weather with PM2.5 as the primary pollutant is commonly known as "smog".

The persistence of smog weather will make many people feel uncomfortable outdoors, but generally speaking, we spend less time outdoors and spend most of our time indoors. But for workers who need to work outdoors for a long time, such as construction workers, sanitation workers, traffic police, etc. They are exposed to smog for a longer time and have a greater exposure. Therefore, it is necessary to emphasize and attach importance to the protection of outdoor workers against haze weather.