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Coping with Vog from Halema'uma'u

(Be sure to also read about Vog from Pu'u Oo on our web site!)

For centuries, Halema’uma’u Crater at the summit of Kilauea has been emitting volcanic gases that include carbon dioxide, sulfur dioxide (SO2), hydrochloric acid, and a variety of other trace gases.  During recent decades, the rate of discharge of sulfur (and the other gases) has varied: during the 1970’s, when Mauna Ulu and several other short-lived eruptions were occurring at Kilauea’s summit, large amounts of gases (including sulfur dioxide) were discharged through Halema’uma’u crater and several vents extending toward Keanakakoi.  The average SO2 emissions from Kilauea’s summit, from 1997 through the first half of 2007, were around 120 metric tonnes per day. However, on March 11, 2008, a new fumarole formed on the floor of Halema’uma’u that increased the sulfur production to an estimated 2,000 - 2,500 tonnes per day. By mid-April, SO2 production had decreased to around 800 tonnes per day. The plume of volcanic gas can be seen on the Hawaiian Volcano Observatory’s webcam.

County vog brochure

Download Hawaii County's brochure addressing the 2008 emissions from Kilauea Volcano.

Plume from Halemaumau

Halemaumau plume is seen above.


Big Island residents are already familiar with vog from Pu’u O’o, which affects different areas of the island depending on wind direction. The vog from Halema’uma’u, likewise, is carried by the wind to a variety of locations, and the direction of the wind is critical.

Halema’uma’u is very close to offices and commercial venues within Hawaii Volcanoes National Park, and only a couple of miles away from Volcano Village. During calm winds, the plume from Halema’uma’u could impact these nearby communities; during southerly winds, the plume could affect much of East Hawaii; and during trade winds, areas in Ka’u  (Pahala, Naalehu, Waiohinu) have been heavily impacted, especially when the particulates get caught in an eddy system and remain in the area instead of being blown out to sea.

Vog on trade wind and south wind days.

Sulfur Dioxide (SO2)

SO2 is a very reactive gas that can cause severe irritation in populations that are sensitive to it. It is soluble in water and forms a weakly acidic solution (sulfurous acid), and easily combines with atmospheric oxygen to form sulfuric acid. Thus, the sulfur compounds in vog will irritate the eyes, throat and lungs, because these are always moist and in contact with air. For people with asthma or other respiratory ailments, the effects of SO2 and other sulfur compounds are more than irritating, and can even be deadly, because they act as strong triggers for airway spasms (constriction) of the bronchial system.  In severely asthmatic individuals, exposure to SO2 can generate such a strong reaction that the individual can no longer breathe without immediate medication to re-open their airways.  Hence, it’s extremely important that, if there is any chance of SO2 exposure to those individuals, both protective devices and medication to counteract the asthmatic response should be readily available at all times.  Even then, it’s wisest to avoid, or leave, areas that are reasonably likely to be impacted by vog in the near future.

Wind Direction determines vog location

There is no way to stop volcanoes from emitting SO2, nor to control wind direction. However, there are several steps you can take to lessen the effects of the volcanic plume on yourself and your family.

  1. Stay indoors, and keep windows and doors shut tightly.
  2. If you have an air conditioner or dehumidifier, these can help to remove SO2 and sulfur aerosols from the air, because both devices condense moisture out of the air that the gases and the aerosol particles will dissolve into.
  3. If you don’t have either of these appliances, you can make your own inexpensive filtration system (pictured below), which uses baking soda (a base) to neutralize airborne sulfur compounds:  as the fan passes room air over the moist baking soda, it will react with the acidic vog to neutralize it and dissolve it into the moisture in the cheesecloth. (Of course, this homemade remedy isn't perfect--but it should help!)

How to use cheesecloth, baking soda,and a fan to combat vog.

If vog is expected to enter your community, the wisest strategy is to relocate to a safer location until the air is free of vog.  Because the winds are so difficult to forecast with accuracy, it’s also advisable to have both current medications as well as a gas/particulate mask available to you at all times.  Even when evacuating, it’s possible that you will have to pass through higher concentrations of vog than are present in your home community so you should carry these items with you as you evacuate.


The Halema’uma’u plume contains not only SO2, but intermittent ash. Ash is composed of particles of rock that are so small  they can be airborne. Whereas SO2 and sulfuric acid are strong chemical irritants, ash has a mechanical, abrasive effect, further irritating the eyes and respiratory tract. If ash starts falling out of the sky in your neighborhood, the best strategy is to shelter indoors and close all the doors and windows. A household air purifier would likely help, since these are designed to reduce dust particulates from the air.  If you have to be outdoors briefly during ash fall, such as to get to your car, you might wear a protective mask, such as a paper dust mask commonly found at hardware stores. But note that particulate masks do not work for vapors—they won’t keep SO2 out. Also, these paper dust masks are intended for larger particle sizes (dust from sanding); the particulates in vog are smaller, and a dust mask won’t be effective on these smaller particles.

In other countries, volcanoes sometimes produce enormous amounts of ash, with disastrous effects on human health. The ash can clog gutters and even collapse roofs, particularly when the ash absorbs rainwater and becomes heavy. Fortunately, so far Halema’uma’u is not producing large quantities of ash. Old-timers on Hawaii island  have a practical approach, and recall sweeping roofs and gutters to clear accumulations of ash and Pele’s hair during past events of Pu’u O’o and Kilauea summit. Homeowners on water catchment systems have additional concerns about SO2 and ashfall; more information is available on our Water Catchement page.


Halema’uma’u’s plume changes from day to day, and wind direction changes periodically. You can deduce where the plume will be by noting the wind direction; the National Weather Service provides a week-long forecast of wind conditions.

The best course of action is:

  1. Have a supply of materials readyfor future events (baking soda, dust masks, respirators, and an emergency evacuation kit)
  2. Plan where you would go (friends, relatives) in case the plume was so thick that your  health was threatened
  3. Keep apprised of current conditions at Halema’uma’u by visiting the USGS-HVO update page


NIOSH provides specific details about sulfur dioxide.

ATSDR answers questions about sulfur dioxide and its effect on human health.

ALAH American Lung Association of Hawaii has helpful suggestions for asthmatics.

Hawaii Volcanoes National Park provides current SO2 conditions.

County of Hawaii has a Kilauea Eruption Update site.

NOAA image of vog