Traces of China’s air pollution have reached southwestern Japan, alarming residents and leading government officials to consider international cooperation to deal with the problem.

Beijing has been suffering severe air pollution this winter, with thick smog blanketing the capital and concentrations of PM 2.5 pollutants exceeding hazardous levels on more than 15 days in January.

Experts say China has failed to regulate air pollutants such as vehicle emissions, which have grown amid the country’s rapid economic development.

PM 2.5 stands for particulate matter with a diameter of 2.5 micrometers or less, which can reach deep into the lungs and blood vessels and cause asthma, heart disease and an increased risk of death.

In Nagasaki Prefecture, PM 2.5 concentrations at four locations, including Sasebo and Isahaya, averaged 41 micrograms per cubic meter on Jan. 31, based on data available by 3 p.m.

It exceeded the standard daily average of 35 micrograms set by the Basic Environment Law.

“The concentration is about one-tenth of that in China and is not expected to immediately affect the body,” a prefectural government official said. “But we may issue an alert if the figure rises substantially.”

The Nagasaki prefectural government has been measuring PM 2.5 concentrations at the four locations since April, and the readings are usually about 20 micrograms per cubic meter a day.

The Fukuoka city government has received about 20 inquiries from citizens since mid-January, when the media reported air pollution coming from China over the East China Sea.

The PM 2.5 concentration measured at six locations in the city all exceeded the government standard of 35 micrograms per cubic meter a day on Jan. 31.

Readings usually exceed the standard on 20 to 30 days a year, according to a city government official.

Beginning in fiscal 2013, the city government plans to announce PM 2.5 concentrations and forecasts to promote awareness. It has already been releasing yellow sand forecasts since March.

In Yamaguchi Prefecture, higher-than-normal concentrations of PM 2.5 have been observed since Jan. 30.

The concentrations were 46 micrograms per cubic meter a day in Ube, 41 micrograms in Sanyo Onoda and above 30 micrograms in six other cities.

Environment ministers from Japan, China and South Korea have met once a year since 1999 to share information and discuss technical cooperation on yellow sand and other issues.

According to the Environment Ministry, officials of the three countries are considering adding PM 2.5 to the agenda.

In Beijing, the PM 2.5 concentration exceeded 250 micrograms per cubic meter a day—a level defined as hazardous by the U.S. Embassy—on more than 15 days in January, and temporarily reached 500 micrograms on Jan. 29.

A Beijing-based diplomat specializing in environmental issues said the situation was totally unexpected, adding that in the United States, hazardous levels are said to be observed only close to wildfires.

According to a study released in December by Peking University and others, 8,500 people would suffer early deaths due to PM 2.5 in Beijing, Shanghai, Guanzhou and Xian, and economic losses would reach 6.8 billion yuan (98 billion yen, or $1.9 billion).

China has failed to regulate PM 2.5 partly because it is produced by many sources, including vehicle emissions and industrial smoke, and because its health impact was understood only recently.

About 5.2 million vehicles travel Beijing’s roads, a 66-percent jump from five years ago. But the capital’s regulations on vehicle emissions and other pollutants are said to be 30 to 40 percent looser than those in Europe.

According to the Beijing News and other sources, the standard for sulfur content in gasoline is 150 ppm or less in most Chinese cities, about 15 times higher than in Japan and Europe.

Beijing city officials say about a quarter of air pollutants drift in from other municipalities, and probably includes pollution from factories relocated to suburbs before the 2008 Beijing Olympics.

Another key source of air pollution is believed to be coal, which has been burnt in stoves without filters amid particularly cold weather this winter.

Air pollutants tend to accumulate in Beijing because the city is situated in a basin. Experts also believe that airflow has stagnated because cooled air close to the ground has remained there.

Kenji Someno, who analyzes environmental issues in China for the Environment Ministry, said the country has made insufficient investments on measures to deal with its air, water and soil pollution and other environmental problems.

Citing a Chinese government report published in 2004, Someno said such investments accounted for a little more than 2 percent of the country’s gross domestic product, compared with the 7 percent the report said was needed.

He added that Japan is said to have invested funds equivalent to more than 8 percent of its GDP in the early 1970s, when the country suffered from serious environmental pollution.

January brought the most frequent occurrences of smog in Beijing since 1954, when statistics became available, and many children have been taken to the hospital due to coughing.

At the Beijing Children’s Hospital on Jan. 31, a man said his baby, less than a year old, had begun coughing despite not having a fever.

“It must have to do with the air pollution,” the father said, irritated.

A chief nurse said many children had come to see doctors because of the air pollution. “Even those who do not go outside have developed bronchitis,” the nurse said.

Masks specifically designed to filter PM 2.5 have sold out at many stores in Beijing over the past few days even though they are more expensive than ordinary masks, at 30 yuan or more each.

A couple was disappointed because they could not find any at a drugstore in the capital’s Dongcheng district.

The husband said his wife, wearing an ordinary mask, had been unable to stop coughing since the day before. The wife, a Beijing native, said air pollution is the price China is paying for rushing its economic development.

According to a manufacturer of PM 2.5-specific masks, its stock of 1.5 million masks has sold out, and sales through the company’s online service reached 2 million yuan in two weeks.