Sharp improvement in Hong Kong’s bad air days attributed to wild weather
Heavy downpours in January and October, usually two of the worst months, help to disperse pollutants
Hong Kong breathed a little easier this year as the number of hours of air pollution reaching “high health risk” and beyond fell by half the recent average.
But much of the decline was due to wetter, windier weather in what are traditionally two of the most polluted months, January and October, according to a study by an environmental group.
Hongkongers were exposed to 1,480 hours of air of high health risk this year, meaning “7” or above on the government’s 11-tier Air Quality Health Index (AQHI), when children, the elderly and those with heart or respiratory illnesses are advised to avoid physical exertion outside and areas with heavy traffic.
About 3,559 hours were logged last year and 4,110 hours in 2014. The yearly average from 2014 to December 20 this year was 3,050 hours. There were also fewer days with high-risk air – 65 compared with 96 in 2014 and 79 in 2015.
Green Power analysed data from the Environmental Protection Department’s 13 general air quality monitoring stations and found “major decreases” in hours of high health risk air in the city’s most polluted towns, including Tuen Mun, Kwai Chung, Yuen Long, Kwun Tong and Tung Chung.
Dr Cheng Luk-ki, head of scientific research and conservation at Green Power, said the worst months for pollution were usually August to October in the autumn seasonal transition as well as January.
“This year the biggest drops whether in hours or days were recorded in October and January.”
Abnormal weather may have been a major factor.
Around 266mm of rain fell in January, 10 times the average of 25mm, according to the Observatory, possibly helping in the dispersal of pollutants. Hong Kong was also affected by five tropical cyclones in October, which brought windier and wetter weather. Rainfall was six times higher than the October average.
Wang Tao, chair professor of atmospheric environment at Polytechnic University – who was not involved in the analysis – said weather and climate changes affected statistical metrics and definitely had a role to play in the drop, as there had been no major reduction in emissions.
A department spokesman cited “efforts to improve air quality in recent years” including the gradual phasing-out of old diesel commercial vehicles, exhaust emissions controls and new laws requiring ships at berth to switch to low-sulphur fuel as playing a role.
But Cheng stressed that air pollution remained stubbornly high in areas such as Tuen Mun, Tung Chung and Yuen Long, all of which had more than 40 days of high-risk air this year, often with ozone or roadside nitrogen oxide concentrations exceeding World Health Organisation safety levels.
“With 65 days of high health risk air, one in every six days is a high health risk. We think this is still considered a serious issue,” Cheng said.
The AQHI, which replaced the Air Pollution Index in 2013, categorises “1” as the lowest risk and a “10+” as the most serious.