The World Health Organisation (WHO) has updated its Air Quality Guidelines for the first time since 2005, slashing the recommended limits of deadly particulate pollution to a fraction of those under Hong Kong’s laws.
The new guidelines, published last night, focus on particulate matter, PM2.5 and PM10, caused by combustion, tyres and brake dust. PM10 can lodge deep into the lungs, while the smallest particles, PM2.5, can enter the bloodstream and brain.
WHO recommends tightening the annual mean of PM2.5 from 10 μg/m3 to 5 μg/m3, around 15% of Hong Kong’s legally permitted level of 35 μg/m3.
The recommended WHO limit for a 24-hour mean of PM2.5 is now 15 μg/m3, a fifth of Hong Kong’s limit of 75 μg/m3.
Hong Kong also allows itself nine “free passes” on that limit over a year, while the WHO recommends only a maximum of three exceedances per year.
Hong Kong will tighten its standards on 1 January, 2022, after a lengthy public consultation in 2019. The new standards will bring annual PM2.5 limits to 25 μg/m3, still five times the new WHO standard; but controversially, the government also increased its allowed number of “free pass” days from nine to 35 days. That’s seven full weeks a year that that the territory may breach its environmental laws without consequence.
At the time, the government said no country had met the WHO Guidelines and it would focus on what was achievable.
In 2019, Hong Kong’s air pollution stations saw 19 exceedances of the PM2.5 limit, while the highest annual pollution, recorded in Causeway Bay, was at 27 μg/m3: over five times the new WHO limit.