The good news is that by later today the vog should lift. The bad news is that it has been really thick lately, obscuring vistas from Diamond Head to Hilo Harbor.

As is typical in the summer, the trade winds disappeared last weekend, but will return by tomorrow, said Jonathan Hoag, a forecaster with the National Weather Service.

"It's rather bad in some areas," Hoag said. "The vog ought to move southward, but it may persist near the Volcano area."

Early yesterday morning at the Jaggar Museum, the sulfur dioxide levels were considered unhealthy at 4:30 a.m. and at 7 a.m. At the Kilauea Visitor Center the sulfur dioxide levels were mostly good to moderate, according to data provided by the National Park Service Web site.

Sulfur dioxide can pose a threat to human, animal and plant life. High levels of sulfur dioxide can cause breathing difficulty and respiratory illness and aggravate existing heart disease in sensitive groups, such as those with asthma, children, the elderly and individuals with heart and lung disease.

Firefighters at the Volcano Fire Station ran their typical four-mile training route yesterday despite the haze, said Capt. George Van Gieson.

"It's hazy, but not all that bad. It's tolerable," Van Gieson said. "We're a quarter-mile from the vent and we're fine."

Just down the way in Hilo, however, Sylvia Dahlby, said the vog was as bad as any smoggy day in Los Angeles.

"This morning it was dreadful," Dahlby said. "It's voggy and it smells like burnt matches. I can't see the ocean from my window and I'm only about a mile from the ocean."

State health officials say that short-term reactions to vog may include difficulty breathing for those with respiratory conditions, as well as itchy eyes and a sore throat. Long-term health effects of vog, or volcanic smog, are largely unknown.

Vog became commonplace this spring when Kilauea's Halema'uma'u crater erupted explosively for the first time since 1924, sending large amounts of sulfur dioxide into the air. As a result, there have been many more voggy days this year. Hawai'i Volcanoes National Park closed twice in April due to high sulfur dioxides levels. Various parts of the park have been closed temporarily.

No parts of the park were closed yesterday because of unhealthy levels of sulfur dioxide.

"Vog just happens," said Janice Okubo, state Department of Health spokeswoman. "There's not much we can do about it. We have monitors in place. It's just because of the weather conditions."