Harmful ozone levels in Hong Kong up 35pc in last 15 years

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.