Dense smog has developed in the north of China, across Beijing and Shanghai, i.e. a distance of 1200 km, equivalent to the distance between Kiel (Germany) and Florence (Italy). The smog appears as a brown to grayish area. The concentration of respirable fine particles was 480 micrograms per cubic metre (µg/m³) in Beijing and 355 in Shanghai that day. The WHO limit for fine particles dangerous to health is 25 µg/m³.