Air pollution in Hong Kong has returned to a "normal level", the government said on Wednesday, with increases in various pollutants recorded since the city got going again after the end of Covid restrictions.

Levels of respirable suspended particulates (PM10), fine suspended particulates (PM2.5), nitrogen dioxide and sulphur dioxide rose slightly in 2023 compared with the year before, the Environmental Protection Department (EPD) said.

The annual average concentration of ozone measured at roadside stations hit a record high.

"That notwithstanding, the air quality in 2023 remains the second best since Hong Kong's return to the motherland," the department said. The best year so far was 2022.

The EPD said emissions were worst in areas with heavy traffic, such as Mong Kok, Sham Shui Po and Kwai Chung, as well as those along Victoria Harbour.

"We have a lot of cars running on the road, and most of them are running on petrol right now, and some of them are using diesel. The emissions are still high, so the government's policy is to try to encourage people to switch to electric cars," said Stephen Siu, an assistant director with the department.

"[Also], emissions from navigation are the major contribution to the nitrogen dioxide emissions in Hong Kong right now, so the government's strategy is to try to tighten the control on the fuel oil used by the vessels to reduce the emissions."

The EPD said the Environment and Ecology Bureau finished reviewing air quality objectives last year, and the authorities will tighten five objectives and set three new parameters according to World Health Organisation guidelines.