A dirty, yellow-brown smog rolled across Tokyo Bay like an inexorable wave on Sunday, March 10, engulfing Yokohama's Bay Bridge, the docks district and the Minato Mirai district of shops, hotels and the largest Ferris wheel in Japan in a haze of dust. What had been a bright spring morning in this coastal city just south of Tokyo had been turned into an afternoon of swirling dirt, with people caught outside choking as they held handkerchiefs to their mouths.

The Japan Meteorological Agency had forecast that the impact of sandstorms in northern China and Mongolia would be felt in the Kanto region surrounding Tokyo over the weekend, although weather patterns have been affecting parts of the country that are closer to mainland China - primarily Kyushu, the most southerly of Japan's main islands - since early February.

News programs displayed multi-colored graphics showing the progress of the clouds of smog as it rolled across Kyushu and the environment ministry said that its website came close to being overloaded as worried residents attempted to find out how serious the problem was going to be in their districts.

Above official standards

On Saturday, the government of Fukuoka City announced that the average amount of a toxic pollutant in the air known as PM2.5 was above the official national environment standard for a second straight day. The standard is set at 35 micrograms per cubic meter, but it reached 42 micrograms and was the third time since February 15 that the level had surpassed the limit.

PM2.5 is defined as particulate matter that measures smaller than 2.5 microns - or a mere 2.5 thousandths of a millimeter. These particles are usually generated by activities that involve the burning of fossil fuels, such as metal processing and other heavy industrial applications, as well as vehicle emissions.

Experts say this form of airborne pollution can trigger inflammatory responses both in the body's respiratory tract and blood vessels. Over time, they say, it can cause thickening of the walls of arteries and associated problems.

"I'm in the centre of Fukuoka City at the moment and it is much clearer today than it has been for some days," Tadashi Manabe, a spokesman for the Fukuoka International Association, told DW. "But I can also see that there is still some haziness in the sky.

"This problem has definitely become a lot worse in recent years and the PM2.5 intensity is very high," he added. "That is because here, we are very much influenced by the wind and the yellow sand that blows into Kyushu from mainland Asia."

Visibility reduced

The pollutants reduced visibility in parts of northern Kyushu to as little as 6 km at the weekend and prompted local authorities to issue a provisional warning for residents to stay indoors as much as possible and to wear masks to avoid inhaling dust when they go outside. They were also warned to not hang laundry outdoors and avoid taking part in sports or other strenuous outdoor activities.

They added that they will issue a formal health warning if levels of PM2.5 reach 70 micrograms per cubic meter.

Cities across southern Japan reported similar conditions, with visibility down to 5 km in Matsue, on the north coast of the main island of Honshu, and estimated at 8 km in Osaka, Kyoto and Nagoya.

Flights were impacted by the reduced visibility, along with high-speed railway services and vehicle traffic on highways.

The sandstorm also apparently contributed to unseasonably high temperatures across the country, with Tokyo reporting a high of 25.3 degrees - the highest reading for March since records were first kept in 1876, national broadcaster NHK said.

'Pollution superpower'

The pollution arriving in Japan has been picked up by local media, with the Shukan Bunshun news magazine describing China as a "pollution superpower" and claiming that the problem is a result of the 300 million tons of nonindustrial waste that is generated in China every year, and only 157 million tons of which is processed appropriately.

The Shukan Taishu weekly magazine suggested that poor air quality was to blame for as many as 300,000 deaths in China every year and a further 600,000 people being hospitalized for respiratory complaints.

Japan and China are already involved in a diplomatic dispute over the sovereignty of a small archipelago of islands that are presently controlled by Tokyo but claimed by Beijing, and neither side wants to worsen the already frayed ties.

The environment ministers of both countries - as well as their counterpart from South Korea, which is also badly affected by emissions from Chinese industry - are scheduled to hold talks in May and seek ways to reduce airborne pollution.