Hong Kong’s air pollution reached the “serious” level today, the highest since June 14, as an approaching typhoon leads to smog, according to a government website.

The pollution level was higher than normal as of 4 p.m., with the Air Quality Health Index reaching the maximum level of 10-plus at 6 monitoring stations, while most stations were at nine or higher, according to a statement on the government’s website. The health risk categories “very high” or “serious,” the statement said.

The light wind has hindered the dispersion of air pollutants and the high level of ozone has promoted the formation of nitrogen dioxide, particularly at street level, according to the press release.

A continental airstream is bringing very hot weather to Guangdong,” according to the release. “The intense sunshine and high temperature enhanced photochemical smog activities and formation of ozone during the daytime, resulting in high background pollution in the region.”

The weather will still be very hot tomorrow under the influence of tropical cyclone Matmo’s outer subsiding airstream, and it is expected the pollution levels would still be higher than normal before then, according to the release.

Poor roadside air quality presents the biggest daily health threat to Hong Kong’s 7.2 million people, according to the government’s clean-air plan published last year. Nitrogen dioxide, mostly formed from vehicles in roadside areas, has been linked to damaged lung function in children and asthma attacks.

via Hong Kong Air Pollution Reaches ‘Serious’ Level on Storm – Businessweek.