Air pollution in parts of Hong Kong reached “serious” levels on Wednesday, and the problem is likely to persist despite scattered thunderstorms over the city.
The news came as the Observatory noted that the city experienced its hottest summer since records started in 1884.
On Wednesday afternoon, the Air Quality Health Index (AQHI) reached the “serious” level – the highest on the government’s scale – at three of the Environmental Protection Department’s 18 monitoring stations, namely those at Tung Chung, Yuen Long and Tuen Mun. All but one of the remaining stations recorded “very high” levels of pollution, while the last one, in the northern New Territories, was at “high”.
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According to the department, the city was experiencing elevated air pollution levels due to the effects of Typhoon Maysak, the strongest typhoon so far this year, which is expected to make landfall in South Korea on Thursday.
Health risk from air pollution in Hong Kong reaches ‘very high’ levels, conditions predicted to persist
“Hong Kong is going through a hot and polluted episode, which is common when there is a typhoon in the region,” said Professor Steve Yim Hung-lam, an air pollution expert at Chinese University.
While ground-level winds remained weak, there was a strong north wind blowing in the upper atmosphere between 600 metres and 2km above the ground, which was bringing in pollutants that settled over the city, Yim explained.
He said the combination of strong sunlight and high maximum temperatures – reaching between 33 and 36 degrees Celsius in some areas, including Chek Lap Kok, near the airport – had also accelerated the formation of ozone, a major air pollutant and greenhouse gas.
Levels of the pollutant at 15 monitoring stations had exceeded the 160-microgram limit laid out in Hong Kong’s Air Quality Objectives, which set concentration limits for pollutants and the number of times the levels can be exceeded in a year. At Tuen Mun, the concentration of ozone hit more than 400 micrograms at 3pm on Wednesday.
The Observatory had issued a very hot weather warning on Wednesday morning, while a thunderstorm warning was also in force.
However, Yim said it was unlikely the isolated rainfall would help with the dispersal of the pollution. “While rain will certainly wash out pollutants like PM2.5 or ozone, it would have to be heavy rain over a large area for it to help with dispersal,” he said. PM2.5 refers to small particulate matter suspended in the air, which can harm lung function.
The Environmental Protection Department expected the AQHI to again be at the “very high” mark on Thursday afternoon.
The air quality index is based on the cumulative health risk caused by average concentrations of four air pollutants: ozone, nitrogen dioxide, sulphur dioxide and particulate matter.
The index is reported on a scale of 1 to 10+, with scores grouped into five health risk categories: low, moderate, high, very high, and serious.
With an AQHI of “very high” or above, the department recommends children, the elderly and people with existing heart or respiratory illnesses to stay indoors and avoid physical exertion, while the general public should also reduce time outdoors.
The city’s meteorological body, meanwhile, said on Wednesday that Hong Kong had recorded a hotter-than-usual August this year. The average temperature last month was 29 degrees Celsius, 0.4 degrees higher than the normal of 28.6 degrees.
“Together with the extremely hot weather in June and July, Hong Kong experienced the hottest summer on record from June to August 2020,” the Observatory statement said.
The number of very hot days recorded this year has already reached 43, which is 32.8 days above the annual norm, breaking the previous record of 38 days set in 2016.