Smog persists across Hong Kong on Wed after authorities warn of ‘serious’ health risk

Unhealthy levels of air pollution have persisted across parts of Hong Kong on Wednesday, after the Environmental Protection Department (EPD) recorded a “serious” level of health risk at monitoring stations on Tuesday.

However, the Observatory said a fresh easterly airstream will arrive at the coast of Guangdong on Wednesday, helping to dissipate the smog.

“Winds are weak over Hong Kong this afternoon, which are unfavourable for pollutant dispersion,” the EPD said in a Tuesday press release. “The intense sunshine enhances photochemical smog activity, leading to the rapid formation of ozone and fine particulates in the Pearl River Delta region. The high ozone level also promotes the formation of nitrogen dioxide.”

See also: Bookmark weatherhongkong.com for weather and air quality updates

According to aqicn.org, which draws upon official data, the Air Quality Index reached 154 in Causeway Bay on Wednesday morning, classified as “unhealthy.” Much of the rest of the territory saw high levels of pollution, classified as “unhealthy for sensitive groups.”

Particulate matter

The EPD’s health risk categories range between “low” and “serious” – the highest level – and track the presence of pollutants including PM2.5 particulates in the atmosphere. “At the ‘Serious’ level, employers of all outdoor workers are advised to assess the risk of outdoor work and take appropriate preventive measures to protect the health of their employees,” the department said.

PM2.5 refers to atmospheric particulate matter measuring less than 2.5 micrometres- about 3 per cent of the diameter of a human hair. As one of the most common units of air quality measurement, studies link PM2.5 to premature mortality, heart or lung diseases, asthma attacks, acute and chronic bronchitis, and other respiratory illnesses.

The main sources of local pollution are marine vessels, motor vehicles and power plants. University of Hong Kong researchers estimate that, in 2024, air pollution led to 3,508 premature deaths in the city and economic losses of HK$42 billion. Those who live in socially deprived areas are more exposed to higher-than-average air pollution levels, an earlier study found. Worldwide, air pollution is linked to 6.7 million premature deaths every year, according to the World Health Organization.

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Tom founded Hong Kong Free Press in 2015 as the city's first crowdfunded newspaper. He has a BA in Communications and New Media from Leeds University and an MA in Journalism from the University of Hong Kong. He previously founded an NGO advocating for domestic worker rights, and has contributed to the BBC, Deutsche Welle, Al-Jazeera and others.

Tom leads HKFP – raising funds, managing the team and navigating risk – whilst regularly speaking on press freedom, ethics and media funding at industry events, schools and conferences around the world.