Roadside air pollution soared to dangerous levels in Hong Kong on Monday as the territory was affected by a continental air stream with high content of pollutants. At noon, air pollution indices taken at roadside monitoring stations hit a “severe” level of 204 in Mong Kok and Central, and reached 144 in Causeway Bay. An API reading exceeding 100 is classified as a “very high” pollution level. Health officials advise that people with heart or respiratory illnesses, the elderly and children reduce physical exertion and outdoor activities, and avoid prolonged stays in streets with heavy traffic. Where the smog comes from and tips on how to survive it The advice extends to healthy people among the general public as well when the reading hits the severe level of 200. Monday’s poor air quality in Hong Kong was due to “a continental air stream with relatively high background air pollution” affecting the city, the Environmental Protection Department said. And the pollutants would not be dispersed until later on Tuesday due to slow winds. “The wind has been light over the last couple of days. The high air pollution incident is caused by the trapping of pollutants, in particular nitrogen dioxide, in the territory,” a spokesman said. According to the Guangdong Provincial Environmental Monitoring Centre, the concentration of air pollutants significantly exceeded national quality in parts of the western Pearl River Delta estuary on Sunday. A regional air quality index compiled by the centre showed the worst hit areas were Zhaoqing, Foshan and Jiangmen prefectures, with pollution readings hitting grades four and five, the two most severe levels on a scale of five. The Hong Kong Observatory expected the city’s API readings to stay high on Monday and Tuesday. It said air quality was expected to improve gradually later on Tuesday when the wind was expected to pick up.