How many levels are there in the dusty weather?

It is divided into five grades: 1. Floating dust: When there is no wind or the average wind speed is less than 3.0m/s, dust floats in the air, and the horizontal visibility is less than 10km. 2. Sand blowing: the wind blows up the dust on the ground, making the air quite turbid, and the horizontal visibility is between 1km and 10km. 3. Sandstorm: Strong winds blow up dust on the ground, making the air very turbid, and the horizontal visibility is less than 1 km. 4. Strong sandstorm: Strong wind blows up dust on the ground, making the air very turbid, and the horizontal visibility is less than 500 meters. 5. Extremely strong sandstorm: Strong wind blows up the dust on the ground, making the air particularly turbid, and the horizontal visibility is less than 50 meters. Remind everyone to go out as little as possible in dusty weather and not to engage in outdoor activities for a long time.