Pollution in skies over Hong Kong hits seven-year high, despite government report saying emissions in decline

The concentration of harmful ozone gas in the Pearl River Delta region is at a seven-year high, raising questions over the validity of a Hong Kong government report that suggested there was a general decline in pollution in the city.

Annual results from the Pearl River Delta Regional Air Quality Monitoring Network, released on Thursday, recorded average ozone concentrations at 58 micrograms per cubic metre last year, the same as in 2017, and the worst since 2011.

The network collates data from 23 monitoring stations in Hong Kong, Guangdong, and Macau, and is part of a joint effort by the governments of the three places to improve air quality in the region.

While the concentration levels of air pollutants of sulphur dioxide (SO2) and respirable suspended particulates (PM10) had decreased by 81 per cent and 36 per cent respectively since 2006, the 2018 ozone concentration levels had gone up by 21 per cent over the same period.

Ozone is formed through a reaction of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the air and under sunlight. It is a main component of photochemical smog, and at elevated levels can cause respiratory diseases.