The Air Quality Health Index (AQHI) at the city’s 15 general and 3 roadside stations all indicated either a “very high” or “serious” health risk to the public on Friday afternoon.
The Environment Protection Department (EPD) said tropical cyclone In-fa, which is moving towards the mainland’s east coast, had brought very hot and hazy weather to the city.
It said light to moderate winds were “bringing an airstream with high regional ozone and particulate background pollutant concentrations”, adding this was not helping to disperse pollution.
“The intense sunshine enhances photochemical smog activity and the rapid formation of ozone and fine particulates in the Pearl River Delta region. The high level of ozone has promoted the formation of nitrogen dioxide,” the EPD said.
Forecasters said pollution levels are likely remain high until a southwesterly airstream brings showers to the coast of southern China next week.
Authorities remind people that when the AQHI is at the “very high” or “serious” levels, children, the elderly and persons with existing heart or respiratory illnesses are advised to reduce outdoor activities to a minimum or avoid such activities altogether.