Central Tokyo air pollution readings neared levels that could require government alerts after thick smog blanketed parts of China for much of this week.

The pollution is originating from both mainland China and Japan, Kansuke Sasaki, an air pollution analyst at the Japan Weather Association said in a telephone interview today.

“The air from the continent arrives directly to Japan more often in the start of spring,” Sasaki said, referring to winds from the Chinese mainland. “That adds to the pollution produced in Japan.”

Readings for particles smaller than 2.5 micrograms in diameter, also known as PM2.5, were at 98 micrograms per cubic meter in Nerima ward and 88 micrograms per cubic meter in Minato ward as of 5 p.m. local time, data on Tokyo’s monitoring website show. That’s more than three times to the World Health Organization’s recommended levels.

Readings of over 80 micrograms per cubic meter before noon would trigger a government warning for citizens to refrain from outdoor activities, according to the environment ministry’s web site.

There was also little wind in places today, which likely made the pollution dense, Sasaki said. The Japan Weather Association is a private company that provides weather forecasts.

China has battled lingering pollution as a consequence of the environmental damage that’s accompanied three decades of double-digit economic growth. Pollution from China’s export manufacturers is traveling across the Pacific Ocean to reach the U.S. West Coast, according to a paper published in the Proceedings of the National Academy of Sciences last month.

The annual average level of PM2.5 in central Tokyo has fallen 55 percent in the 10 years since 2001 as the government has taken measures to curb pollution, according to the Tokyo government. The pollution arriving to Japan from overseas is reaching to levels that can’t be ignored, Sasaki said.

Public broadcaster NHK said earlier that 10 prefectures, including Osaka, issued PM2.5 alerts yesterday, with 9 of 10 issuing the alert for the first time.

via Tokyo Air Pollution Climbs, Approaches Government Alert Levels – Bloomberg.