After pollution readings reached dangerous levels yesterday, Tung Chung is facing further hazardous air over the weekend – unless rain can clear the skies.

Readings from both the World Air Quality Index, also known as AQICN, and the Hong Kong government Air Quality Health Index (AQHI) hit hazardous levels yesterday.

Tung Chung recorded on the AQICN chart of ‘very unhealthy’ for four hours, which it describes as ‘emergency conditions’ in which all people are urged to stay indoors.

The AQHI showed Tung Chung reaching the ‘serious’ level, for six hours up to 7pm yesterday evening – one of six locations around Hong Kong to do so.

Tung Chung air, Wednesday (AQHI)

AQICN says that while today is likely to be merely ‘unhealthy for sensitive groups,’ it predicts extended periods of ‘unhealthy or very unhealthy’ over the weekend and Monday.

More bad air (AQICN)

The AQHI forecast is for “low to very high” risk today.

In a statement issued 11am yesterday EPD called on children and elderly to stay indoors and for the general public to avoid strenuous outdoor activity:

Higher than normal levels of nitrogen dioxide and particulates have been recorded in the territory since early this morning. Hong Kong is being affected by an airstream with higher background pollutant concentrations. In addition, light wind hinders effective dispersion of air pollutants. Sunshine enhances photochemical smog activity and the formation of ozone and fine particulates, resulting in today’s high pollution in the vicinity of Hong Kong. The high level of ozone has promoted the formation of nitrogen dioxide, particularly in parts of the urban areas and at the roadside.

However, it noted that the pollution levels could ease with the rain patches predicted for Friday.

At 9:30am Tung Chung air was rated moderate on the AQICN index.

Earlier this week the EPD released data that showed the number of unhealthy air days last year had nearly doubled over 2016. The department attributed this to warmer weather and lower cloud cover, making it easier for ozone.