Highest level of hazardous ozone in two decades recorded in Hong Kong in 2018, despite overall improved air quality
- Warmer temperatures, combined with less cloud cover and rain, contributed to the rise, says the Environmental Protection Department
- Air quality improved last year, with the government planning to continue with emission reduction targets and increase use of clean fuel
Hong Kong got its highest average annual concentrations of hazardous ozone in nearly two decades last year, officials have said.
And people in Yuen Long, Tuen Mun and Tung Chung were breathing the unhealthiest air, according to air quality data released by the Environmental Protection Department on Friday.
This could be the result of weather conditions such as more sunshine, less cloud cover and rain, and slightly warmer temperatures.
These conditions made it more favourable for ozone – one of the most harmful types of air pollution, which can cause respiratory diseases – to form, which it does through chemical reactions, especially in sunlight.
Clocking in at 52 micrograms per cubic metre, the ozone figure was slightly up on 2017’s record high of 51mcg. Roadside levels also rose, from 23 mcg per cubic metre to 24 mcg per cubic metre.
And the department said a reduction in certain motor emissions could actually have worsened the ozone situation.
Dave Ho Tak-yin, assistant director of environmental protection, said on Friday the ozone rise “could be attributed to high regional background ozone and a fall in local [emissions of nitrogen dioxides (NOx)] from vehicles, which results in less nitric oxide (NO) to react with and remove ozone”.
“So even if we reduce the amount of NOx emissions, it doesn’t necessarily mean that the ozone level will be lowered,” he said.
But Patrick Fung Kin-wai, chief executive of local green group the Clean Air Network, was not convinced by that reasoning.
“This isn’t the first time we have heard about the theory. While what was said about the chemical reaction is true, this isn’t a new finding so I don’t think the drop in emissions levels justifies why Hong Kong’s ozone level keeps worsening,” he said.
“It’s actually been a few years, since 2016 as I recall, that the ozone level has been going up, so what is taking the administration so long to figure out a solution?”
Fung added that any delay to such a solution threatened Hongkongers’ health. He urged the administration to set an agenda on how it plans to work with mainland Chinese authorities to solve the regional environmental issues.
But the record-high level of ozone was not the only problem.
Dominant nitrogen dioxide (NO2) – which emanates from motor vehicles, especially diesel-powered ones – was down on 2017, but still above the government’s target level.
Roadside concentrations of NO2 fell 4.8 per cent to 82mcg per cubic metre, still more than double the annual air quality objective target of 40mgc.
Tuen Mun had the worst air quality, recording 51 days in which readings on the 11-tier Air Quality Health Index were at 7 or higher.
Yuen Long, Tung Chung and Causeway Bay got 42 days of 7 or above.
On the bright side, the department said the overall air quality in the city improved last year.
Hourly health risk levels graded high or above were recorded at general stations on 2.1 per cent of days; down from 3 per cent in 2017.
And all 13 monitoring stations in the city saw a drop in the number of days when the level hit 7 or above.
Principal environmental protection officer Kenneth Leung Kai-ming ruled out the possibility that the pollution could have been caused by building work on major infrastructure in the region, including the Hong Kong-Zhuhai-Macau Bridge.
But he admitted that the level of ozone was subject to strong regional influence, such as smog coming from Guangdong province.
Data from the department showed that from 2013 to 2018 the concentrations of major pollutants including particulate matter (PM2.5 and PM10), nitrogen dioxide and sulphur dioxide in ambient air fell by 28 per cent, to 54 per cent of the air quality objectives limit.
The concentrations of the same pollutants at roadsides have fallen to 36 per cent of the limits, a 32 per cent dip from five years ago.
The government also announced that it planned to review its emission-reduction targets, transport planning and management, and use of clean fuel.
The measures were likely to produce results by 2025, the department promised.