Volcano Watch — Kīlauea sulfur dioxide emissions down by 90%

The smell of sulphur is strong but not unpleasant to the sinner
Mark Twain, 1866

Sinners or not, many of us living on the island of Hawai`i over the past decade feel that, although we cherish the volcanoes, the smell of sulfur gas and volcanic air pollution, or vog, from Kīlauea has become decidedly unpleasant.

Currently, we are experiencing the clean air quality that many residents and visitors remember from before 1986, when the Kīlauea east rift zone eruption became continuous, and a daily, steady supply of gas accumulated, rather than being dispersed by the winds.

Lately, air in leeward Hawai`i has been very clear, with little volcanic haze to obscure the view of the mountains and coastal areas. Interrupted trade winds usually cause east Hawai`i to be inundated with large amounts of sulfur dioxide (SO₂) gas and sulfate particles from Kīlauea. During a recent interruption in trade winds, however, levels of ambient SO₂ measured near the summit of Kīlauea were significantly lower than what has become `normal' for the last 10 years.

This period of better air quality is a direct result of the low level of current eruptive activity. After the collapse of Pu`u `O`o and the start of eruptive episode 54 early in the morning on January 30, east rift zone SO<sub>2</sub> gas emissions were 15-30% of the 2,000 tons per day or so that we have measured during eruptively active periods over the last several years. When the short-lived episode ended on January 31, SO<sub>2</sub> emissions decreased even further. Although there is lava ponding, once again, within Pu`u `O`o, current SO₂ emissions from Kīlauea appear to be less than 10% of the daily emission rates measured since 1993.

This 90% decrease in released SO₂ gas from Kīlauea is very good news for Kona residents, for it means that there is simply much less gas to be blown by the prevailing trade winds from degassing sources on Kīlauea around South Point, and up along the Kona coast, where it is trapped by the onshore-offshore daily wind regime. On this journey, there is also less gas to react chemically with sunlight, oxygen, dust and water to form the sulfuric acid and other sulfate particles that cause the visible pollution that had become so ubiquitous for Kona residents and visitors.

The significant decrease in SO₂ gas emissions is good news for east Hawai`i residents too. During periods of interrupted trade winds, areas from Volcano to lower Puna to Hilo, and even Hamakua, can be impacted by vog. Residents living close to the gas emission sources at the summit and middle east rift zone, have periodically experienced high levels of SO<sub>2</sub> gas. At a site near the park headquarters in Hawai`i Volcanoes National Park, ambient concentrations of SO₂ exceeded the EPA primary health standard of 0.139 parts per million on nearly 70 occasions over the past 10 years.

Residents and visitors alike should enjoy this interlude of cleaner air, for it is presently unclear whether the current low level of activity at Kīlauea will persist. Since roughly 8 pounds of SO₂ gas bubbles out from each cubic yard of magma as it rises toward the surface to erupt as lava, a lower eruption rate of lava releases less gas, which, in turn, will produce less vog.

There have been periods of little (1894-1907) or no activity (1934-1952) at Kīlauea since the start of the historic period in 1790. Since the 1950s, however, eruption rates have increased dramatically, with rates for each ensuing decade surpassing those of the previous decade. So, although the vog `problem' has largely disappeared for now, it is probable that we will once again be faced with high vog episodes on the Big Island in the future.

The health effects of vog are not well documented, although anecdotal reports from health-care professionals and other Big Island residents include headaches, fatigue, respiratory difficulties, and allergy complications during extended periods of poor air quality. Studies from urban areas with pollution of similar composition show that acidic aerosols, such as those comprising vog, can degrade lung function and compromise our immune systems, especially for vulnerable individuals, such as children, the elderly, and asthmatics.

In pursuing the goal of obtaining relevant information on vog, the Hawai`i State Department of Health has engaged scientists from the University of Hawai`i, and University of Southern California medical school to examine the health effects of vog on school children. At the U.S. Geological Survey's Hawaiian Volcano Observatory, we are continuing to improve our measurements of the source of the vog. An extended lull in eruptive activity, like the one we are currently experiencing, can be beneficial to health studies by providing a sharp contrast to periods of bad air quality. We all look forward to the fruits of this research.