http://www.scmp.com/news/hong-kong/article/1722475/harmful-ozone-levels-hong-kong-35pc-last-15-years
Ernest Kaoernest.kao@scmp.com
Thick smog hangs over Hong Kong in January last year. Photo: AFP
The concentration of ozone in the city's air has increased by a third in the last 15 years, highlighting yet again the severity in regional air pollution, preliminary government data has shown.
But despite the uptick, the Environmental Protection Department pointed to notable drops in most pollutants, including nitrogen dioxide, sulphur dioxide and breathable particulates, including double-digit percentage decreases at roadside stations last year from 2013.
Ozone concentrations at general stations, however, were still up 7 per cent to 46 micrograms per cubic metre of air last year.And between 1999 and 2014, concentrations of ambient ozone at the city's general air quality monitoring stations rose by a staggering 35 per cent.
"This once again shows this is an area that needs improvement" via regional cooperation, said Mok Wai-chuen, the department's assistant director of environmental protection. He said emissions control measures would allow the city to meet its 2020 air quality goals.
Last year's most severe pollution hit districts in the northwestern New Territories such as Tung Chung, Yuen Long and Tuen Mun, all three of which experienced more than 450 hours of pollution that was classified as high, very high or serious on the Air Quality Health Index.
The general average was 342 hours.
Hong Kong has set a target to reduce highly toxic nitrogen oxides and volatile organic compounds by 20 to 30 per cent and 15 per cent, respectively, by the year 2020 in accordance with a regional air quality management plan between Hong Kong and Guangdong.
Ozone is a major component of photochemical smog that not only reduces visibility but also threatens human health when exposure is prolonged and high. The pollutant is formed by a reaction between volatile organic compounds and nitrogen oxides generated from other combustion sources.
Mok attributed the improvements to vehicle emission control policies coming into effect, including a plan to progressively phase out 82,000 diesel commercial vehicles that predate European emission standards introduced in 2005, known as Euro IV.
Some environmental groups welcomed the government's new data but said average concentrations were still high and far from satisfactory. The Clean Air Network said there were 148 days last year where the level of sulphur dioxide was higher than the World Health Organisation's 24-hour safety standard.
Citing a dip in pollution late last year, Friends of the Earth said the 79-day Occupy movement in autumn could have had something to do with the overall improved roadside air quality.
"It shows that controlling the number of vehicles on the roads is more effective" than regulating their emissions, the group said in a statement. The department has not provided final fourth-quarter figures.
