What does the symbol with eight across it mean in the weather forecast?

In the weather forecast, the horizontal symbol of 8 is smog, the yellow 8 warning signal indicates moderate, and the orange 8 warning signal indicates severe.

As a natural phenomenon, smog has three factors. First, the phenomenon of static wind in the horizontal direction has increased; Second, the phenomenon of vertical inversion; The third is the increase of suspended particulate matter. With the development of industry, the increase of motor vehicles, the discharge of pollutants and the increase of suspended solids in the city directly lead to the decrease of visibility and make the whole city look gray.

There are four regions with severe haze weather in China: Huanghuaihai region, Yangtze River basin, Sichuan basin and Pearl River Delta.

Extended data:

Haze classification

1, mild haze: air relative humidity is less than or equal to 80%, visibility is more than or equal to 5km and less than10km;

2. Mild haze: the relative humidity of the air is less than or equal to 80%, and the visibility is more than or equal to 3 kilometers and less than 5 kilometers;

3. Moderate haze: the air relative humidity is less than or equal to 80%, and the visibility is more than or equal to 2 kilometers and less than 3 kilometers;

4. Severe haze: the air relative humidity is less than or equal to 80%, and the visibility is less than 2 kilometers.

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