The clear skies brought early this morning by last night’s rain are not set to last until the weekend, with an unhealthy cloud of air pollution forecast to choke Hong Kong.
The Environmental Protection Department said in a statement on Thursday it had “recorded a gradual increase in pollution levels since this morning”.
“It is expected that the Air Quality Health Index at some general and roadside air quality monitoring stations may reach the ‘serious’ level later today,” it added.
“Serious” is the top level of air pollution on the index’s five-tier scale, which also includes “low”, “moderate”, “high” and “very high”.
By noon, only one of the city’s 16 monitoring stations, a roadside one in Central, reported a “high” level, the others remaining “moderate”.
In Central, concentrations of nitrogen dioxide and carbon monoxide reached 170.4 micrograms per cubic metre and 924.3mcg/m³ respectively.
The department said high concentrations of pollutants such as ozone and particulates had been recorded in Hong Kong since Thursday morning, as the fine and hot weather enhanced photochemical smog activity.
“The high level of ozone has also promoted the formation of nitrogen dioxide,” the department said.
The Hong Kong Observatory forecast the anticyclone which had brought the hot weather would remain in force on Friday.
“It is expected that pollution levels will remain higher than normal until the advent of stronger wind next week,” the department added.
With a health risk category in the “very high” range or above, children, the elderly and people with heart or respiratory illnesses are advised to keep physical exertion and outdoor activity to a minimum.
The general public is advised to reduce time outdoors, especially in areas with heavy traffic.