The Environmental Protection Department has recorded higher than normal pollution levels today, and warns it may get worse.
At 3pm the Air Quality Health Index at several general and all roadside air monitoring stations reached "8" or above, corresponding to the "Very High" health risk category.
The department said Hong Kong is being affected by an airstream with higher background pollutant concentrations.
Intense sunshine enhances photochemical smog activities and the formation of ozone, resulting in higher pollution in the region, it said, adding light winds have hindered effective dispersion of air pollutants.
The high level of ozone has promoted the formation of nitrogen dioxide, particularly in parts of the urban area and at roadsides. The department warned that the health index of some general and roadside air monitoring stations may reach "Serious" level later today.
The Hong Kong Observatory has forecast mainly fine and very hot weather for the next two days and expects pollution levels to remain higher than normal until a broad trough of low pressure brings unsettled weather later this week.
Children, the elderly and people with heart or respiratory illnesses are advised to avoid physical exertion and outdoor activities, especially in areas with heavy traffic.
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