SEOUL — The heavy haze that settled over Seoul and much of South Korea last week is here to stay, at least for part of the week.

The haze is caused by pollution, stagnant air, and no recent weather systems to clear it out, said Lt. Kevin Bourne, chief of operations and training for the 607th Weather Squadron.

"Basically, you get a stagnant air mass, and all the pollution kind of collects," he said.

He said the haze is not the kind caused by yellow sand that migrates eastward from Chinese and Mongolian deserts and may include heavy metals from factories and developments.

Im Jang-ho, spokesman for the Korean Meteorological Administration, said the haze will continue for several days but rain should clear it out by the end of next week. The haze limits visibility and people should avoid outdoor activities, he said.

U.S. Forces Korea had issued no health alerts as of Friday afternoon. Air quality levels in Seoul were considered "moderate," meaning people at high risk — the elderly, children, and those with heart or lung disease — should avoid heavy exertion outdoors.