SASEBO NAVAL BASE, Japan — A eye-stinging combination of desert sand and pollution from China has been creating an unhealthy haze at Sasebo Naval Base and the rest of southwestern Japan for nearly two weeks, and the forecast calls for more of the same through spring.

“I’ve never seen it like this,” base spokesman Charles Howard said Tuesday. Howard is a retired Navy Master Chief who has been in Sasebo for the better part of the past 16 years.

Still, it was business as usual at Sasebo on Tuesday despite air pollution levels rising into the Environmental Protection Agency’s “unhealthy” range.

Base officials lack the equipment to test air quality and must rely on alarms raised by their Japanese counterparts. Japanese officials only issue warnings in the morning, and since pollution levels were low in Sasebo between 5-7 a.m., none were issued even though conditions deteriorated throughout the day. So sailors walked with infants in strollers, people jogged and recess was held outside at Defense Department schools despite the elevated risk.

“We rely on our military partners,” said Charles Hoff, a spokesman for Defense Department schools in the Pacific. “We’re definitely sensitive to the issue. All we can do is respond when we have information to respond to.”

Eastern China, South Korea and Japan have been affected by bouts of so-called “yellow haze” blowing in from central China for years. The latest one has blanketed western Japan from Kyoto prefecture to the island of Kyushu.

It’s made up of yellow sand from China’s deserts and a pollutant, known as PM2.5, that attaches itself to the sand, according to Japan’s Fukuoka District Meteorological Observatory. The sands are lifted by ascending air currents and carried to Japan by subtropical westerly winds.

PM2.5 particles are about one 30th the width of a human hair and can reach deep inside the lungs, according to Japan’s Environment Ministry website. It poses various health risks, especially to those with respiratory ailments, such as asthma and bronchitis, and at-risk populations such as children and the elderly, and could even contribute to lung cancer and heart attacks.

Environment Ministry safety guidelines say residents should be warned to stay inside when PM2.5 levels exceed 70 micrograms per cubic meter on a daily average. Nagasaki prefecture has a policy to warn its residents when the average level exceeds 85 between 5-7 a.m. on any given day.

On Tuesday, Fukuishi, south of Sasebo, registered 11 and Daito, to the southwest, registered 10, so no warning was issued, an official from Sasebo city’s environmental department said. However, as the day progressed, visibility dropped from 19-25 miles on average to less than six, and air quality deteriorated significantly.

Daito hit 73 micrograms per cubic meter at 10 a.m., and Fukuishi registered 82 at 4 p.m.

Japanese authorities did issue a warning Tuesday morning for Iki and Tsushima islands, which tested at 96 — the prefecture’s first warning since implementing the safety guidelines in February, the city official said. Iki island is about 60 kilometers north of Sasebo.

The EPA’s Air Quality Index ranges from 0-500, with 101-150 deemed “unhealthy for sensitive groups.” Over 150 is “unhealthy,” over 200 is “very unhealthy” and over 300 is “hazardous.”

The standard is the same used as the Japanese government, base officials said.

On Tuesday, the AQI for PM2.5 in Daito peaked at 154 and 160 at Fukuishi, according to websites that track pollution and weather that were provided by base officials. Levels hovered around 100 Wednesday morning, passing into the “unhealthy for sensitive groups” range at one point before dropping.

Over the past two weeks, base officials have occasionally issued updates on their Facebook page. On Tuesday, they shared links to air quality monitoring websites and the EPA’s instruction regarding air quality but did not issue a warning or safety instructions.

Nagasaki prefecture’s warning told residents in the affected region — particularly those with respiratory and cardiovascular problems, children and the elderly — to stay home and not to go out if possible, and minimize the amount of intense exercise outside, according to a statement. Officials said the pollution could last throughout the remainder of spring.

Local AQI readings can be tracked online and to see the pollution in real time visit the Japan Meteorological Agency.

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