Haze Over Shanghai and Yangtze River Mouth, China31.2N 121.4E
Haze hangs in the air over Shanghai (bottom right), the mouth of the Yangtze River and the surrounding area. Haze refers to weather with air humidity of 80 percent or below, and is different from fog, which occurs when humidity in the air is more than 90 percent. It forms when concentrations of dust and smog in the air are high.
Shanghai, like Beijing, classifies haze as light, moderate or heavy. Light haze means that outdoor visibility is between five and ten kilometers; with moderate haze, visibility is between two and five kilometers; heavy haze means visibility is less than two kilometers.
Experts said that haze contains substances harmful to the respiratory tract and lungs so people should stay indoors during moderate and heavy haze days. Long exposure to haze can lead to coryza, bronchitis and even lung cancer.