‘Dr. Vog’ says the smog’s not gone, Maui’s monitors tell a different story

At the start of this week, airplane pilots landing on Maui said they had never experienced these kinds of winds—tailwinds swirling to headwinds in the final approach. Usually, they come in with the tradewinds at their backs; this time, the birds were being pushed around as the winds shifted rapidly from trades to Konas.

Particulate matter coming from Hawaiʻi Island’s Kīlauea volcano told a similar story this week. First, the wind brought it—but these unwelcome chemicals just don’t seem to want to leave.

According to atmospheric scientist Dr. Steven Businger—colloquially known as “Dr. Vog”—the Hawaiian Islands have been stuck in a historically voggy funk, reminiscent of the vog during the devastating 2018 eruption at Kīlauea’s East Rift Zone.

The vog, or volcanic smog, he said, is a result of Kīlauea’s eruptions in its west Halemaʻumaʻu crater at intervals lasting about 12 hours each with frequent fountaining reaching hundreds of feet into the air. Then, to complicate matters, the islands have been locked in a stagnant weather pattern with very light winds.

“The vog is kind of circling around and getting trapped,” Businger said. “It tends to be in higher concentrations near the trade wind inversion, so as you go uphill on Haleakalā, the vog will be more concentrated.”

While emission rates from Kīlauea have recently been “high”—up to 50,000 metric tons of sulfur dioxide (SO₂) per day, according to Businger and recent USGS reports—Maui’s air quality sensors appear to be telling a different story.

On Friday afternoon, for example, the official monitors showed “moderate” air quality in Kīhei and “good” in Kahului.

“That means it’s really bad,” Businger said, only half joking.

And while the air might technically meet EPA standards, Businger said that can mean little to people suffering real effects. “People’s sensitivity can range greatly. Some aren’t affected much. Others are sent to the emergency room. Even very low levels of vog can make people very, very unhappy.”

Another issue: what’s actually being measured. Vog is mostly made up of SO₂ and its chemical byproduct, sulfate aerosol (SO₄), but only certain compounds are being tracked.

“SO₂ is a gas. SO₄ is a particle,” Businger said. “The SO₂ gets converted to SO₄ in the atmosphere, and those particles are small—tiny enough to pass deep into your lungs. Once there, they can grow in size, because they’re hydroscopic. There’s a lot of moisture in your lungs.”

On the official dashboards, the only measurement consistently showing up is PM2.5—a measure of fine particulate matter that includes dust, diesel exhaust, and some volcanic particles.

But that reading alone, Businger said, can be misleading.

“PM2.5 does not specifically measure sulfate aerosol. It includes particles from many sources. Half of vog might be SO₂ and half might be SO₄. If you’re not measuring SO₂, then you have no idea how high that is.”

Adding to that, both of Maui’s air sensors are located near sea level, where vog levels tend to be lower due to the “Maui vortex,” a pattern that stagnates air on the west side of Haleakalā.

The solution, he said, is more—and better—monitoring.

“But good luck getting more monitors under the current climate,” he added.

For those still asking, “How bad is the vog?” Businger offered a different metric for comparison.

New data shows the 2018 Kīlauea eruption emitted nearly 200,000 tons of SO₂ per day. The most recent eruption on April 2 released up to 50,000 tons per day. For comparison, one of the tallest smokestacks in the history of the world emitted about 5,000 tons of SO₂ daily at its peak.

According to official comments from the Hawaiʻi State Department of Health (DOH) on April 7, the vog episode was “moderate to heavy” for all of Maui County, for over one week due to light persistent southerly (Kona) winds.

“Vog is usually heaviest in central Maui especially along Haleakalā between Kīhei and Kula because cloud cover along Haleakalā creates an inversion there,” the DOH said. “However, for the past week the vog has been heavy along west Maui, Molokaʻi and Lanaʻi in addition to central Maui.”

The department said the recent historic concentrations of particulates in Hawaiʻi had been less than those in 2018, which saw the highest concentrations of vog on record.

To reduce the impacts of vog, Businger suggests the following:

• Stay Indoors
• Run Air Conditioners
• HEPA Air Filters 
• Reduce Activity
• Wear mask or bandana over mouth and nose

The current on-and-off eruption began on Dec. 23, with each burst lasting anywhere from 13 hours to 8 days, followed by quiet periods ranging from less than a day to nearly two weeks, according to the US Geological Survey’s Hawaiian Volcano Observatory.

The most-recent 16th episode saw fountains reaching past 700 feet. Each of the prior 15 episodes since Dec. 23 have also fountained, with peak fountains exceeding 1,000 feet in height.

View the latest Hawaiʻi Department of Health vog advisory, posted Feb. 28, 2025, here. The Hawaiʻi Interagency Vog Information Dashboard can be accessed here.

**Editor’s Note: This story was updated April 8, 2025, to add new comments from the Hawaiʻi State Department of Health.