CAMP RED CLOUD, South Korea — Yellow dust levels spiked to critical levels Sunday and Monday in the midst of U.S. Forces Korea’s largest annual exercise, according to the 18th Medical Command and the Korean Meteorological Administration.

Dust levels at Chinhae Naval Base, Camp Walker in Daegu and Camp Carroll in Waegwan all registered levels well above the 18th Medical Command’s “hazardous” ratings on Sunday and Monday morning, according to the command’s Web site.

Sunday marked the official beginning of the Key Resolve/Foal Eagle exercise, although some of the thousands of off-peninsula servicemembers who participate have been arriving and preparing for the past couple of weeks.

Camp Walker and Camp Carroll areas experienced a high of 1,428 micrograms per cubic meter of the yellow dust, which comes from the Chinese and Mongolian deserts and may include heavy metals from factories and developments. Chinhae dust levels reached 1,190 micrograms at 4 a.m. Monday before coming down to acceptable levels later in the day.

At 800 micrograms per cubic meter, the 18th Medical Command’s Yellow Dust Web site recommends that everyone stay indoors and keep activity low.

USFK monitors yellow sand levels closely and sends out information to commanders when levels rise, said USFK public affairs officer Col. Franklin Childress.

“I’m not aware of a situation where it got so high where we had to stop training,” Childress said. “Commanders on the ground have to assess it and take appropriate action.”

The Marine and Navy compound at Camp MuJuk in Pohang also recorded “very unhealthy” levels of dust Sunday night, according to the medical command Web site.

Kunsan Air Base recorded unhealthy levels of dust at 332 micrograms Sunday but returned to low levels Monday.

All other major bases in South Korea, including the northern ranges where soldiers and Marines conduct much of their outdoor training, experienced no more than moderate dust levels less than 199 micrograms.

At those levels, the 18th Medical Command recommends less physical exertion only for people at high risk of illness.

South Korean officials took cautious steps until the yellow dust storm, known to Koreans as the “hwangsa,” dissipated in the southern parts of the peninsula Monday.

“The entrance ceremonies [for the new semester] at the kindergarten and elementary schools around Busan were postponed until [Tuesday], and the schools are closed today due to the strong hwangsa,” said weather forecaster Park Gwang-ho of the Korean Meteorological Administration.

Park told Stars and Stripes Monday that the peninsula can expect more yellow dust storms than average in the coming months.

Higher temperatures and dry weather in the China and Mongolian deserts allow the dust to rise with easterly winds.

Yongsan Garrison and other areas were hit with yellow dust storms exceeding 2,000 micrograms in 2006.

Korean weather officials then predicted above-average numbers of yellow dust storms in 2007. Instead, a surprisingly wet spring in China kept dust storms in check.

For updates on the latest yellow dust counts at bases in South Korea, go to http://www.seoul.amedd.army.mil/sites/yellowsand/default.asp

Hwang Hae-rym contributed to this report.