Air quality in Hong Kong improves but pollution levels expected to remain higher than normal for rest of week
After a day of pollution levels posing a ‘very high’ health risk on Wednesday, the air quality improved at night
Parts of Hong Kong were blanketed in bad air earlier on Wednesday, with pollution levels posing a “very high” health risk at five of 16 air quality monitoring general and roadside stations as of 7pm.
Kwai Chung, Tsuen Wan, Yuen Long, Tuen Mun and Tai Po had readings of 10 – the second-highest level on the index – meaning that the amounts of nitrogen dioxide and ozone recorded there were higher than normal.
Other stations, with the exception of Tap Mun, had readings of 8 or 9, meaning there was also a “very high” health risk in those areas.
But after thunderstorms and rain fell across the city, the air quality improved by 9pm, with the index falling to between 4 and 6 at all stations. A thunderstorm warning remained in force on Wednesday night.
Deteriorating air quality earlier in the day had prompted the Environmental Protection Department to issue a notice at about 4.40pm, warning the situation could worsen.
“Hong Kong is being affected by an air mass with higher background pollutant concentrations,” it stated. “In addition, the light wind hinders effective dispersion of air pollutants. The sunshine enhances photochemical smog activity and the formation of ozone and fine particulates, resulting in high pollution in the Pearl River Delta region.”
The Observatory said there would still be light winds in the following days and this meant pollution levels would remain higher than normal.
Ozone concentrations on Wednesday evening exceeded the WHO’s guidelines of 100 micrograms per cubic metre of air.
The Post reported on Tuesday that local ozone pollution had surged 20 per cent since 2013, reaching a two-decade high while concentrations of major pollutants had dropped.
Ozone is formed when nitrogen oxides and volatile organic compounds – emitted from vehicles, industrial activities and power plant emissions – mix in the air under sunlight. It is closely linked to regional pollution and sources of volatile organic compounds can come from anywhere within the Pearl River Delta.
Lam Chiu-ying, the former Hong Kong Observatory chief, said the situation on Wednesday afternoon was “very serious”, with many areas recording ozone values of more than 200mcg per cubic metre of air.
This phenomenon usually happened around August and September, when there were typhoons in the vicinity.
“It is unavoidable that this phenomenon happens a few times each year. But in recent years, it happens more,” he said. “It is also getting more serious.”
“Very high” pollution levels were detected for three hours in Yuen Long and Tai Po in July. The situation was worse in June, with 85 hours of very polluted air.
Pollution levels were deemed “serious” – hitting 10+ on the index – several months ago in January.
When the air quality is bad, the elderly, children and people with existing heart or respiratory diseases should reduce or avoid physical exertion and outdoor activities, the department’s notice said.
The Education Bureau also urged schools to refer to its website to learn more about measures to safeguard students’ health. Employers were advised to assess the risks of employees working outdoors and take preventive measures.